diff --git a/.dir-locals.el b/.dir-locals.el
new file mode 100644
index 0000000..3f538f5
--- /dev/null
+++ b/.dir-locals.el
@@ -0,0 +1,8 @@
+;; TODO: We have to be careful what variables we set here. Some can cause the
+;;       Eldev linters to not read the settings here. See emacs-eldev/eldev#83.
+((nil
+  ;; FIXME: This is just set to silence linter line-length warnings. It should
+  ;;       be set to an intentional value, then the long-lines fixed.
+  (fill-column . 136)
+  (indent-tabs-mode . nil)
+  (sentence-end-double-space . nil)))
diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..bdc4c7a
--- /dev/null
+++ b/.envrc
@@ -0,0 +1,2 @@
+direnv_layout_dir="$PWD/.cache/direnv"
+use flake
diff --git a/.github/renovate.json b/.github/renovate.json
new file mode 100644
index 0000000..3c7598b
--- /dev/null
+++ b/.github/renovate.json
@@ -0,0 +1,10 @@
+{
+    "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+    "extends": ["config:base"],
+    "lockFileMaintenance": {
+        "enabled":true
+    },
+    "nix": {
+        "enabled":true
+    }
+}
diff --git a/.gitignore b/.gitignore
index ccc9fd9..5076318 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,5 @@
-*.DS_Store
\ No newline at end of file
+*.elc
+/.cache/direnv/
+/dist
+/.eldev
+/result
diff --git a/Eldev b/Eldev
new file mode 100644
index 0000000..6fc3a32
--- /dev/null
+++ b/Eldev
@@ -0,0 +1,30 @@
+;;; Eldev --- Build configuration -*- mode: emacs-lisp; lexical-binding: t; -*-
+
+(require 'eldev)
+(require 'elisp-lint)
+
+(define-error 'auto-dark-test-invalid-test-selection "Unknown test type")
+
+(eldev-add-loading-roots 'test "initialize")
+
+(eldev-defoption auto-dark-test-selection (type)
+  "Select tests to run; type can be `main' or `integration'"
+  :options        (-T --test-type)
+  :for-command    test
+  :value          TYPE
+  :default-value  'main
+  (pcase (intern type)
+    ('main
+     (setf eldev-test-fileset
+           `(:and ,eldev-test-fileset (:not "./tests/initialization"))))
+    ('integration (setf eldev-test-fileset "./tests/initialization"))
+    (_ (signal 'auto-dark-test-invalid-test-selection (list type)))))
+
+(setq
+ ;; run all linters by default
+ eldev-lint-default t
+ ;; ignore lisp files in the example directory
+ eldev-standard-excludes `(:or ,eldev-standard-excludes "./example")
+ ;; and disable the ‘elisp-lint’ validators that are already covered by
+ ;; ‘eldev-lint’ (see ‘eldev-linter-elisp’).
+ elisp-lint-ignored-validators '("checkdoc" "package-lint"))
diff --git a/README.md b/README.md
index be8920a..b4be0b4 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,11 @@
 
 
 [![MELPA](https://melpa.org/packages/auto-dark-badge.svg)](https://melpa.org/#/auto-dark)
+[![MELPA Stable](https://stable.melpa.org/packages/auto-dark-badge.svg)](https://stable.melpa.org/#/auto-dark)
 
+[![built with garnix](https://img.shields.io/endpoint.svg?url=https%3A%2F%2Fgarnix.io%2Fapi%2Fbadges%2FLionyxML%2Fauto-dark-emacs%3Fbranch%3Ddevelopment)](https://garnix.io/repo/LionyxML/auto-dark-emacs)(dev)
+
+[![built with garnix](https://img.shields.io/endpoint.svg?url=https%3A%2F%2Fgarnix.io%2Fapi%2Fbadges%2FLionyxML%2Fauto-dark-emacs)](https://garnix.io/repo/LionyxML/auto-dark-emacs)(master)
 
 Do you want Emacs to follow your MacOS/Linux/Windows/Android dark-mode on/off
 options?
@@ -28,7 +32,7 @@ Install it from [MELPA](https://melpa.org/#/auto-dark) and add to your
 
 ```emacs-lisp
 (require 'auto-dark)
-(auto-dark-mode t)
+(auto-dark-mode)
 ```
 
 
@@ -40,7 +44,7 @@ and then add the following to your `.emacs`:
 ```emacs-lisp
 (add-to-list 'load-path "~/.emacs.d/auto-dark/")
 (require 'auto-dark)
-(auto-dark-mode t)
+(auto-dark-mode)
 ```
 
 Or use `use-package` to install:
@@ -48,7 +52,7 @@ Or use `use-package` to install:
 
 ```emacs-lisp
 (use-package auto-dark
-  :config (auto-dark-mode t))
+  :init (auto-dark-mode))
 ```
 
 
@@ -61,7 +65,7 @@ If you use Spacemacs, add `(auto-dark)` to the
 
 ```emacs-lisp
 (use-package auto-dark
-  :init (spacemacs/defer-until-after-user-config (lambda () (auto-dark-mode t)))
+  :init (spacemacs/defer-until-after-user-config #'auto-dark-mode)
   :defer t)
 ```
 
@@ -72,8 +76,15 @@ built-in theme loading logic.
 ### Doom Emacs
 
 If you're under Doom Emacs, the following configuration should be
-enough:
+enough[^1]:
 
+[^1]: There is possibly an issue with Doom Emacs’ initialization, where the
+“Loading a theme can run Lisp code. Really load?” prompt can cause
+initialization to fail. Auto-Dark attempts to ensure that this prompt doesn’t
+occur during initialization, but it isn’t perfect. If this causes a problem for
+you, try setting `custom-safe-themes` to `t` in your config before setting
+`auto-dark-themes`. But be aware that this is a potential security concern. See
+the documentation of `custom-safe-themes` for more details.
 
 ```emacs-lisp
 ;; In your packages.el
@@ -83,16 +94,15 @@ enough:
 
 (after! doom-ui
   ;; set your favorite themes
-  (setq! auto-dark-dark-theme 'doom-one
-        auto-dark-light-theme 'doom-one-light)
-  (auto-dark-mode 1))
+  (setq! auto-dark-themes '((doom-one) (doom-one-light)))
+  (auto-dark-mode))
 ```
 
 
 ## Notes for MacOS users
 
 From the box, this package takes advantage of some built-in functionality found
-on the formulaes [Emacs Plus](https://github.com/d12frosted/homebrew-emacs-plus) 
+on the formulaes [Emacs Plus](https://github.com/d12frosted/homebrew-emacs-plus)
 and [Emacs Mac](https://github.com/railwaycat/homebrew-emacsmacport?tab=readme-ov-file)
 to make detecting switches faster.
 
@@ -116,7 +126,7 @@ by going to:
 
 
 ```
-Settings -> Privacy & Security -> Emacs -> System Events 
+Settings -> Privacy & Security -> Emacs -> System Events
 ```
 
 
@@ -142,47 +152,50 @@ Following, a complete configuration with all settings set to its defaults:
 ```emacs-lisp
 (use-package auto-dark
   :ensure t
-  :config 
-  (setq auto-dark-dark-theme 'wombat)
-  (setq auto-dark-light-theme 'leuven)
-  (setq auto-dark-polling-interval-seconds 5)
-  (setq auto-dark-allow-osascript nil)
-  (setq auto-dark-allow-powershell nil)
-  ;; (setq auto-dark-detection-method nil) ;; dangerous to be set manually
-
-  (add-hook 'auto-dark-dark-mode-hook
-    (lambda ()
-      ;; something to execute when dark mode is detected))
-
-  (add-hook 'auto-dark-light-mode-hook
-    (lambda ()
-      ;; something to execute when light mode is detected))
-
-  (auto-dark-mode t))
+  :custom
+  (auto-dark-themes '((wombat) (leuven)))
+  (auto-dark-polling-interval-seconds 5)
+  (auto-dark-allow-osascript nil)
+  (auto-dark-allow-powershell nil)
+  ;; (auto-dark-detection-method nil) ;; dangerous to be set manually
+  :hook
+  (auto-dark-dark-mode
+   . (lambda ()
+        ;; something to execute when dark mode is detected
+        ))
+  (auto-dark-light-mode
+   . (lambda ()
+        ;; something to execute when light mode is detected
+        ))
+  :init (auto-dark-mode))
 ```
 
 
 A short description of each setting:
 
 
-#### `auto-dark-dark-theme`
-
-The theme to enable when dark-mode is active.
+#### `auto-dark-themes`
 
+A list containing two elements. The first is the list of themes to enable when
+dark-mode is active and the second is the list of themes to enable when
+dark-mode is inactive.
 
-Possible values are themes installed on your system found by
-`customize-themes` or `nil` to use Emacs with no themes (default
-appearance).
 
+Possible values for each sublist are themes installed on your system found by
+`customize-themes` or `nil` to use Emacs with no themes (default appearance).
 
-#### `auto-dark-light-theme`
 
-The theme to enable when dark-mode is inactive.
+If this variable is `nil`, then the set of themes from `custom-enabled-themes`
+will be used for both dark and light mode. These themes must support
+`frame-background-mode`, or else there will be no visible change.
 
 
-Possible values are themes installed on your system found by
-`customize-themes` or `nil` to use Emacs with no themes (default
-appearance).
+**NB**: When adding themes to this list, switching between light and dark, or
+initializing Emacs, you may see a prompt like “Loading a theme can run Lisp
+code. Really load?” If you answer “yes” and allow Emacs to treat the theme as
+safe in future sessions, you should only see this prompt once per theme. To
+disable the prompt completely, you can set `custom-safe-themes` to `t` before
+setting `auto-dark-themes`.
 
 
 #### `auto-dark-polling-interval-seconds`
@@ -261,4 +274,3 @@ This package in action:
 - Linux (Gnome DE)
 
 ![auto-dark-emacs in action - linux gnome](images/demo_gnome.gif)
-
diff --git a/auto-dark.el b/auto-dark.el
index 367b530..4dda3f5 100644
--- a/auto-dark.el
+++ b/auto-dark.el
@@ -1,11 +1,12 @@
-;;; auto-dark.el --- Automatically sets the dark-mode theme based on macOS/Linux/Windows status -*- lexical-binding: t; -*-
+;;; auto-dark.el --- Automatically set the dark-mode theme based on system status -*- lexical-binding: t; -*-
 
 ;; Author: Rahul M. Juliato
 ;;         Tim Harper <timcharper at gmail dot com>
 ;;         Vincent Zhang <seagle0128@gmail.com>
 ;;         Jonathan Arnett <jonathan.arnett@protonmail.com>
+;;         Greg Pfeil <greg@technomadic.org>
 ;; Created: July 16 2019
-;; Version: 0.12
+;; Version: 0.13.2
 ;; Keywords: macos, windows, linux, themes, tools, faces
 ;; URL: https://github.com/LionyxML/auto-dark-emacs
 ;; Package-Requires: ((emacs "24.4"))
@@ -37,15 +38,19 @@
   :group 'tools
   :prefix "auto-dark-*")
 
-(defcustom auto-dark-dark-theme 'wombat
-  "The theme to enable when dark-mode is active."
-  :group 'auto-dark
-  :type '(choice symbol (const nil)))
+(defun auto-dark--initialize-after-init (&optional initialize-fn)
+  "Return a function suitable for passing to `defcustom'’s :initialize parameter.
+The returned function defers initialization to `after-init-hook'. INITIALIZE-FN
+is the function that should be used to eventually initialize the symbol. It
+defaults to `custom-initialize-reset', as does :initialize itself."
+  (let ((init-fn (or initialize-fn #'custom-initialize-reset)))
+    (lambda (symbol exp)
+      (if after-init-time
+          (funcall init-fn symbol exp)
+        (add-hook 'after-init-hook (lambda () (funcall init-fn symbol exp)))))))
 
-(defcustom auto-dark-light-theme 'leuven
-  "The theme to enable when dark-mode is inactive."
-  :group 'auto-dark
-  :type '(choice symbol (const nil)))
+(make-obsolete-variable 'auto-dark-dark-theme 'auto-dark-themes "0.13")
+(make-obsolete-variable 'auto-dark-light-theme 'auto-dark-themes "0.13")
 
 (defcustom auto-dark-polling-interval-seconds 5
   "The number of seconds between which to poll for dark mode state.
@@ -80,13 +85,13 @@ doing!"
 
 (defvar auto-dark--dbus-listener-object nil)
 
-(defun auto-dark--is-dark-mode-applescript ()
+(defun auto-dark--current-mode-applescript ()
   "Invoke AppleScript using Emacs built-in AppleScript support.
 In order to check if dark mode is enabled.  Return true if it is."
   (if (fboundp 'ns-do-applescript)
-      (auto-dark--is-dark-mode-ns)
+      (if (auto-dark--is-dark-mode-ns) 'dark 'light)
     (if (fboundp 'mac-do-applescript)
-        (auto-dark--is-dark-mode-mac)
+        (if (auto-dark--is-dark-mode-mac) 'dark 'light)
       (error "No AppleScript support available in this Emacs build.  Try setting `auto-dark-allow-osascript` to t"))))
 
 (defconst auto-dark--is-dark-mode-applescript
@@ -96,15 +101,22 @@ It is “true” if the system is in dark mode, and “false” otherwise.")
 
 (defun auto-dark--is-dark-mode-ns ()
   "Check if dark mode is enabled using `ns-do-applescript'."
-  ;; `ns-do-applescript' doesn’t support booleans, so we convert to an integer.
-  (/= 0
-      (ns-do-applescript (concat auto-dark--is-dark-mode-applescript
-                                 " as integer"))))
+  ;; FIXME: We shouldn’t need to check `fboundp' on every call, just when
+  ;;        setting the detection method.
+  (when (fboundp 'ns-do-applescript)
+    ;; `ns-do-applescript' doesn’t support booleans, so we convert to an
+    ;; integer.
+    (/= 0
+        (ns-do-applescript (concat auto-dark--is-dark-mode-applescript
+                                   " as integer")))))
 
 (defun auto-dark--is-dark-mode-mac ()
   "Check if dark mode is enabled using `mac-do-applescript'."
-  (string-equal "true"
-                (mac-do-applescript auto-dark--is-dark-mode-applescript)))
+  ;; FIXME: We shouldn’t need to check `fboundp' on every call, just when
+  ;;        setting the detection method.
+  (when (fboundp 'mac-do-applescript)
+    (string-equal "true"
+                  (mac-do-applescript auto-dark--is-dark-mode-applescript))))
 
 (defun auto-dark--is-dark-mode-osascript ()
   "Invoke AppleScript using Emacs using external shell command;
@@ -112,19 +124,24 @@ this is less efficient, but works for non-GUI Emacs."
   (equal '("true")
          (process-lines "osascript" "-e" auto-dark--is-dark-mode-applescript)))
 
-(defun auto-dark--is-dark-mode-dbus ()
+(defun auto-dark--current-mode-dbus ()
   "Use Emacs built-in D-Bus function to determine if dark theme is enabled."
-  (eq 1 (caar (dbus-ignore-errors
-                (dbus-call-method
-                 :session
-                 "org.freedesktop.portal.Desktop"
-                 "/org/freedesktop/portal/desktop"
-                 "org.freedesktop.portal.Settings" "Read"
-                 "org.freedesktop.appearance" "color-scheme")))))
+  (pcase (caar (dbus-ignore-errors
+                 (dbus-call-method
+                  :session
+                  "org.freedesktop.portal.Desktop"
+                  "/org/freedesktop/portal/desktop"
+                  "org.freedesktop.portal.Settings" "Read"
+                  "org.freedesktop.appearance" "color-scheme")))
+    (0 nil)
+    (1 'dark)
+    (2 'light)))
 
 (defun auto-dark--is-dark-mode-powershell ()
   "Invoke powershell using Emacs using external shell command."
-  (string-equal "0" (string-trim (shell-command-to-string "powershell -noprofile -noninteractive \
+  (string-equal "0"
+                (string-trim (shell-command-to-string
+                              "powershell -noprofile -noninteractive \
 -nologo -ex bypass -command Get-ItemPropertyValue \
 HKCU:\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize \
 -Name AppsUseLightTheme"))))
@@ -132,14 +149,21 @@ HKCU:\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize \
 (defun auto-dark--is-dark-mode-winreg ()
   "Use Emacs built-in Windows Registry function.
 In order to determine if dark theme is enabled."
-  (eq 0 (w32-read-registry 'HKCU
-			   "Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize"
-			   "AppsUseLightTheme")))
+  ;; FIXME: We shouldn’t need to check `fboundp' on every call, just when
+  ;;        setting the detection method.
+  (when (fboundp 'w32-read-registry)
+    (eq 0
+        (w32-read-registry
+         'HKCU
+         "Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize"
+         "AppsUseLightTheme"))))
 
 (defun auto-dark--is-dark-mode-termux ()
-  "Use Termux way to determine if dark theme is enabled.  ref: https://github.com/termux/termux-api/issues/425."
+  "Use Termux way to determine if dark theme is enabled.
+ref: https://github.com/termux/termux-api/issues/425."
   (string-equal "Night mode: yes"
-                (shell-command-to-string "echo -n $(cmd uimode night 2>&1 </dev/null)")))
+                (shell-command-to-string
+                 "echo -n $(cmd uimode night 2>&1 </dev/null)")))
 
 (defvar auto-dark-dark-mode-hook nil
   "List of hooks to run after dark mode is loaded." )
@@ -147,60 +171,112 @@ In order to determine if dark theme is enabled."
 (defvar auto-dark-light-mode-hook nil
   "List of hooks to run after light mode is loaded." )
 
-(defun auto-dark--is-dark-mode ()
-  "If dark mode is enabled."
-  (pcase auto-dark-detection-method
-    ('applescript
-     (auto-dark--is-dark-mode-applescript))
-    ('osascript
-     (auto-dark--is-dark-mode-osascript))
-    ('dbus
-     (auto-dark--is-dark-mode-dbus))
-    ('powershell
-     (auto-dark--is-dark-mode-powershell))
-    ('winreg
-     (auto-dark--is-dark-mode-winreg))
-    ('termux
-     (auto-dark--is-dark-mode-termux))))
+(defun auto-dark--current-system-mode ()
+  "Return our best guess of the mode the system is in.
+It can be dark, light, or nil."
+  (or (pcase auto-dark-detection-method
+        ('applescript
+         (auto-dark--current-mode-applescript))
+        ('osascript
+         (if (auto-dark--is-dark-mode-osascript) 'dark 'light))
+        ('dbus
+         (auto-dark--current-mode-dbus))
+        ('powershell
+         (if (auto-dark--is-dark-mode-powershell) 'dark 'light))
+        ('winreg
+         (if (auto-dark--is-dark-mode-winreg) 'dark 'light))
+        ('termux
+         (if (auto-dark--is-dark-mode-termux) 'dark 'light)))
+      (frame-parameter nil 'background-mode)
+      ;; Let Emacs guess what the background should be.
+      (frame-terminal-default-bg-mode nil)
+      ;; Give up and just use the value we last set
+      auto-dark--last-dark-mode-state
+      (lwarn 'auto-dark
+             :warning
+             "couldn’t determine current system appearance")))
+
+(defun auto-dark--initialized-p ()
+  "Check whether initialization is far enough along to change themes."
+  (and (boundp 'auto-dark-themes)
+       (or auto-dark-themes
+           (and (boundp 'auto-dark-dark-theme)
+                (boundp 'auto-dark-light-theme)))))
 
 (defun auto-dark--check-and-set-dark-mode ()
   "Set the theme according to the OS's dark mode state.
 In order to prevent flickering, we only set the theme if we haven't
 already set the theme for the current dark mode state."
-  (let ((appearance (if (auto-dark--is-dark-mode) 'dark 'light)))
-    (unless (eq appearance auto-dark--last-dark-mode-state)
-      (auto-dark--set-theme appearance))))
+  ;; This can be called during custom variable initialization, so ensure we only
+  ;; do it once we’re certain initialization is far enough along.
+  (when (auto-dark--initialized-p)
+    (let ((appearance (auto-dark--current-system-mode)))
+      (unless (and (eq appearance auto-dark--last-dark-mode-state)
+                   (equal custom-enabled-themes
+                          (auto-dark--themes-for-mode appearance)))
+        (auto-dark--set-theme appearance)))))
 
 (defun auto-dark--update-frame-backgrounds (appearance)
   "Set the `frame-background-mode' for all frames to APPEARANCE."
   (setq frame-background-mode appearance)
   (mapc #'frame-set-background-mode (frame-list)))
 
+(defun auto-dark--enable-themes (&optional themes)
+  "Re-enable THEMES, which defaults to ‘custom-enabled-themes’.
+This will load themes if necessary."
+  (interactive)
+  (let ((full-themes (remq 'user
+                           (delete-dups (or themes custom-enabled-themes)))))
+    ;; Disable only the themes we’re not going to re-enable.
+    (mapc (lambda (theme)
+            (unless (memq theme full-themes)
+              (disable-theme theme)))
+          custom-enabled-themes)
+    (let ((failures (mapcan (lambda (theme)
+                              (condition-case nil
+                                  ;; Enable instead of load when possible.
+                                  (if (custom-theme-p theme)
+                                      (enable-theme theme)
+                                    (load-theme theme))
+                                (:success nil)
+                                (error (list theme))))
+                            (reverse full-themes))))
+      (when failures
+        (warn "Failed to enable theme(s): %s"
+              (mapconcat #'symbol-name failures ", "))))))
+
+(defun auto-dark-toggle-appearance ()
+  "Switch between light and dark mode.
+If `auto-dark-detection-method' is nil, this will persist until the next time
+this is called. Otherwise, it could switch to the system appearance at any
+time."
+  (interactive)
+  (auto-dark--set-theme (if (eq auto-dark--last-dark-mode-state 'dark)
+                            'light
+                          ;; NB: This does _something_ even if we don’t know
+                          ;;     what the previous state was, since the user
+                          ;;     explicitly requested a change.
+                          'dark)))
+
 (defun auto-dark--set-theme (appearance)
   "Set light/dark theme Argument APPEARANCE should be light or dark."
-  (mapc #'disable-theme custom-enabled-themes)
-  (setq auto-dark--last-dark-mode-state appearance)
-  (pcase appearance
-    ('dark
-     (when auto-dark-light-theme
-       (disable-theme auto-dark-light-theme))
-     (auto-dark--update-frame-backgrounds 'dark)
-     (when auto-dark-dark-theme
-       (load-theme auto-dark-dark-theme t))
-     (run-hooks 'auto-dark-dark-mode-hook))
-    ('light
-     (when auto-dark-dark-theme
-       (disable-theme auto-dark-dark-theme))
-     (auto-dark--update-frame-backgrounds 'light)
-     (when auto-dark-light-theme
-       (load-theme auto-dark-light-theme t))
-     (run-hooks 'auto-dark-light-mode-hook))))
+  ;; This can be called during custom variable initialization, so ensure we only
+  ;; do it once we’re certain initialization is far enough along.
+  (when (auto-dark--initialized-p)
+    (setq auto-dark--last-dark-mode-state appearance)
+    (auto-dark--update-frame-backgrounds appearance)
+    (auto-dark--enable-themes (auto-dark--themes-for-mode appearance))
+    (run-hooks (pcase appearance
+                 ('dark 'auto-dark-dark-mode-hook)
+                 ('light 'auto-dark-light-mode-hook)))))
 
 (defvar auto-dark--timer nil)
 (defun auto-dark-start-timer ()
   "Start auto-dark timer."
   (setq auto-dark--timer
-        (run-with-timer 0 auto-dark-polling-interval-seconds #'auto-dark--check-and-set-dark-mode)))
+        (run-with-timer 0
+                        auto-dark-polling-interval-seconds
+                        #'auto-dark--check-and-set-dark-mode)))
 
 (defun auto-dark-stop-timer ()
   "Stop auto-dark timer."
@@ -212,6 +288,8 @@ already set the theme for the current dark mode state."
 Ask D-Bus to send us a signal on theme change and add a callback
 to change the theme."
   (setq auto-dark--dbus-listener-object
+        ;; Documented at
+        ;; https://flatpak.github.io/xdg-desktop-portal/docs/doc-org.freedesktop.portal.Settings.html
         (dbus-register-signal
          :session
          "org.freedesktop.portal.Desktop"
@@ -221,7 +299,10 @@ to change the theme."
          (lambda (path var val)
            (when (and (string= path "org.freedesktop.appearance")
                       (string= var "color-scheme"))
-             (auto-dark--set-theme (pcase (car val) (0 'light) (1 'dark) (2 'light))))))))
+             (pcase (car val)
+               (0 nil)
+               (1 (auto-dark--set-theme 'dark))
+               (2 (auto-dark--set-theme 'light))))))))
 
 (defun auto-dark--unregister-dbus-listener ()
   "Unregister our callback function with D-Bus.
@@ -234,7 +315,8 @@ Remove theme change callback registered with D-Bus."
    ((auto-dark--use-ns-system-appearance)
     (add-hook 'ns-system-appearance-change-functions #'auto-dark--set-theme))
    ((auto-dark--use-mac-system-appearance)
-    (add-hook 'mac-effective-appearance-change-hook #'auto-dark--check-and-set-dark-mode))
+    (add-hook 'mac-effective-appearance-change-hook
+              #'auto-dark--check-and-set-dark-mode))
    ((auto-dark--use-dbus)
     (auto-dark--register-dbus-listener))
    (t (auto-dark-start-timer))))
@@ -245,7 +327,8 @@ Remove theme change callback registered with D-Bus."
    ((auto-dark--use-ns-system-appearance)
     (remove-hook 'ns-system-appearance-change-functions #'auto-dark--set-theme))
    ((auto-dark--use-mac-system-appearance)
-    (remove-hook 'mac-effective-appearance-change-hook #'auto-dark--check-and-set-dark-mode))
+    (remove-hook 'mac-effective-appearance-change-hook
+                 #'auto-dark--check-and-set-dark-mode))
    ((auto-dark--use-dbus)
     (auto-dark--unregister-dbus-listener))
    (t (auto-dark-stop-timer))))
@@ -268,8 +351,8 @@ Remove theme change callback registered with D-Bus."
    ((and (eq system-type 'darwin)
          (or (fboundp 'ns-do-applescript)
              (fboundp 'mac-do-applescript))
-		 (or (eq window-system 'ns)
-			 (eq window-system 'mac)))
+         (or (eq window-system 'ns)
+             (eq window-system 'mac)))
     'applescript)
    ((and (eq system-type 'darwin)
          auto-dark-allow-osascript)
@@ -290,7 +373,9 @@ Remove theme change callback registered with D-Bus."
    ((eq system-type 'windows-nt)
     'winreg)
    (t
-    (error "Could not determine a viable theme detection mechanism!"))))
+    (lwarn 'auto-dark :error "Could not determine a viable theme detection \
+mechanism! You can use ‘auto-dark-toggle-appearance’ to manually switch between \
+modes."))))
 
 ;;;###autoload
 (define-minor-mode auto-dark-mode
@@ -301,11 +386,106 @@ Remove theme change callback registered with D-Bus."
   (if auto-dark-mode
       (progn
         (unless auto-dark-detection-method
-          (setq auto-dark-detection-method (auto-dark--determine-detection-method)))
+          (setq auto-dark-detection-method
+                (auto-dark--determine-detection-method)))
         (auto-dark--check-and-set-dark-mode)
         (auto-dark--register-change-listener))
     (auto-dark--unregister-change-listener)))
 
-(provide 'auto-dark)
+(defun auto-dark--set-individual-theme-var (symbol theme)
+  "Pre-load THEME and assign it to SYMBOL.
+This also updates Auto-Dark’s state as necessary."
+  ;; Pre-load this theme (to force prompts for ‘custom-safe-themes’ while
+  ;; the user is interacting with Auto Dark, rather than at
+  ;; initialization or ‘frame-background-mode’ charge).
+  (when (and theme (not (custom-theme-p theme)))
+    (load-theme theme nil t))
+  (set-default symbol theme)
+  (when auto-dark-mode
+    ;; Make sure Auto Dark is showing the updated themes for the current
+    ;; ‘frame-background-mode’.
+    (auto-dark--check-and-set-dark-mode)))
+
+(defcustom auto-dark-dark-theme 'wombat
+  "The theme to enable when dark-mode is active.
 
+This variable is obsolete. You should set `auto-dark-themes' instead."
+  :group 'auto-dark
+  :type '(choice symbol (const nil))
+  :initialize (auto-dark--initialize-after-init)
+  :set #'auto-dark--set-individual-theme-var)
+
+(defcustom auto-dark-light-theme 'leuven
+  "The theme to enable when dark-mode is inactive.
+
+This variable is obsolete. You should set `auto-dark-themes' instead."
+  :group 'auto-dark
+  :type '(choice symbol (const nil))
+  :initialize (auto-dark--initialize-after-init)
+  :set #'auto-dark--set-individual-theme-var)
+
+;; Dark & light themes need to be set together because enabling and disabling
+;; themes modifies `custom-enabled-themes', so if only one mode were expected to
+;; default to `custom-enabled-themes', it would use the wrong list of themes
+;; after the first time the other mode enables its themes.
+(defcustom auto-dark-themes nil
+  "The themes to enable for dark and light modes.
+The default is to use the themes in `custom-enabled-themes', but that only works
+if the themes are aware of `frame-background-mode', which many aren’t.
+
+If your themes aren’t aware of `frame-background-mode' (or you just prefer
+different themes for dark and light modes), you can set explicit lists of themes
+for each mode. Like with `custom-enabled-themes', the earlier themes in the list
+have higher precedence.
+
+One other thing to be aware of is that when you first load a theme, you may be
+prompted to acknowledge that the theme can run arbitrary Lisp code.
+Acknowledging this and then allowing Emacs to treat the theme as safe in future
+sessions will silence the prompt (for that particular theme). If you would just
+prefer to ignore this warning for all themes, you can set `custom-safe-themes'
+to t."
+  :group 'auto-dark
+  :type '(choice
+          (const :tag "Use custom-enabled-themes" nil)
+          (list :tag "Use distinct dark & light lists"
+                (repeat :tag "Dark" symbol)
+                (repeat :tag "Light" symbol)))
+  :set (lambda (symbol value)
+         ;; Pre-load any themes used by Auto Dark (to force prompts for
+         ;; ‘custom-safe-themes’ while the user is interacting with Auto Dark,
+         ;; rather than at initialization or ‘frame-background-mode’ charge).
+         (mapc (lambda (mode-themes)
+                 (mapc (lambda (theme)
+                         (unless (custom-theme-p theme)
+                           (load-theme theme nil t)))
+                       mode-themes))
+               value)
+         (set-default symbol value)
+         (when auto-dark-mode
+           ;; Make sure Auto Dark is showing the updated themes for the current
+           ;; ‘frame-background-mode’.
+           (auto-dark--check-and-set-dark-mode)))
+  :version "0.13")
+
+(defun auto-dark--themes-for-mode (mode)
+  "Return the set of themes to be used in MODE.
+MODE should be light or dark. If none of the Auto-Dark theme variables are set,
+this returns nil, which means that `custom-enabled-themes' will be used as the
+theme list."
+  (let ((patched-themes (or auto-dark-themes
+                            (if (and custom-enabled-themes
+                                     (not (equal custom-enabled-themes
+                                                 (list auto-dark-dark-theme)))
+                                     (not (equal custom-enabled-themes
+                                                 (list auto-dark-light-theme))))
+                                '(() ())
+                              (list (list auto-dark-dark-theme)
+                                    (list auto-dark-light-theme))))))
+    ;; TODO: Once `auto-dark-dark-theme' and `auto-dark-light-theme' are
+    ;;       removed, the function can be reduced to this form.
+    (pcase mode
+      ('dark (car patched-themes))
+      ('light (cadr patched-themes)))))
+
+(provide 'auto-dark)
 ;;; auto-dark.el ends here
diff --git a/example/home.nix b/example/home.nix
new file mode 100644
index 0000000..b4cdd7c
--- /dev/null
+++ b/example/home.nix
@@ -0,0 +1,7 @@
+{lib, ...}: {
+  programs.emacs = {
+    enable = true;
+    extraConfig = lib.readFile ./init.el;
+    extraPackages = epkgs: [epkgs.auto-dark];
+  };
+}
diff --git a/example/init.el b/example/init.el
new file mode 100644
index 0000000..d32c16e
--- /dev/null
+++ b/example/init.el
@@ -0,0 +1,23 @@
+;;; init.el --- An example configuration -*- lexical-binding: t; -*-
+
+;; We recommend customizing variables before enabling modes, to avoid
+;; “flickering” of values being set to their defaults initially, and then
+;; updated. `custom-set-variables' is very fast unless the associated package
+;; has already been loaded, in which case it may execute arbitrary code. So,
+;; doing this first ensures that you get to the rest of your initialization
+;; quickly, which can then be done in an order that matters to you.
+(custom-set-variables
+ '(auto-dark-themes '((tsdh-dark) (tsdh-light))))
+
+;; The earlier you enable modes that affect the UI, the better, as these can
+;; also cause flickering from the system defaults to the package configuration.
+;; Unfortunately, this can’t generally be done in early-init, which would
+;; otherwise allow the initial display of the frame to use the UI configuration.
+(auto-dark-mode 1)
+
+;; Non-UI initialization should go here.
+
+;; `use-package' is also a good way to configure Auto-Dark. It’s built-in on
+;; Emacs 29+, but must be installed on earlier versions.
+
+;;; init.el ends here
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..8e50117
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,335 @@
+{
+  "nodes": {
+    "bash-strict-mode": {
+      "inputs": {
+        "flake-utils": [
+          "flaky",
+          "bash-strict-mode",
+          "flaky",
+          "flake-utils"
+        ],
+        "flaky": [
+          "flaky"
+        ],
+        "nixpkgs": [
+          "flaky",
+          "bash-strict-mode",
+          "flaky",
+          "nixpkgs"
+        ],
+        "shellcheck-nix-attributes": "shellcheck-nix-attributes"
+      },
+      "locked": {
+        "lastModified": 1722346313,
+        "narHash": "sha256-qxIzt/0BCP9LlVE1Lze/2qlM5eZ8X5hQk4E6ghiBF5w=",
+        "owner": "sellout",
+        "repo": "bash-strict-mode",
+        "rev": "098ffd0f072b3b7b3e84d9c524d18d6c62f64a47",
+        "type": "github"
+      },
+      "original": {
+        "owner": "sellout",
+        "repo": "bash-strict-mode",
+        "type": "github"
+      }
+    },
+    "flake-schemas": {
+      "locked": {
+        "lastModified": 1701189173,
+        "narHash": "sha256-ieQZLjqfvOP+52WeMdkD/x5njEIAqjKuAc/jnmruaoc=",
+        "owner": "sellout",
+        "repo": "flake-schemas",
+        "rev": "68727227a8f349fe0831f6389d9a91064637b70c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "sellout",
+        "ref": "patch-1",
+        "repo": "flake-schemas",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "inputs": {
+        "systems": [
+          "flaky",
+          "systems"
+        ]
+      },
+      "locked": {
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "flaky": {
+      "inputs": {
+        "bash-strict-mode": "bash-strict-mode",
+        "flake-utils": "flake-utils",
+        "garnix-systems": "garnix-systems",
+        "home-manager": "home-manager",
+        "nixpkgs": "nixpkgs",
+        "project-manager": "project-manager",
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1727247261,
+        "narHash": "sha256-J8nCKfPj04uYb11xWY1fKzlXkdXewoAIEBQRtqwCy8g=",
+        "owner": "sellout",
+        "repo": "flaky",
+        "rev": "daccb2cff4d0322b600c106b0ea9f1f9152dcd4f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "sellout",
+        "repo": "flaky",
+        "type": "github"
+      }
+    },
+    "garnix-systems": {
+      "locked": {
+        "lastModified": 1723225755,
+        "narHash": "sha256-y17fVgb4LJheN4VDsHCmZRHrOJwKj8oUPvXk2FqUOnI=",
+        "owner": "garnix-io",
+        "repo": "nix-systems",
+        "rev": "c2466c5c1d3591933b4389868902e2f47a47fadb",
+        "type": "github"
+      },
+      "original": {
+        "owner": "garnix-io",
+        "repo": "nix-systems",
+        "type": "github"
+      }
+    },
+    "home-manager": {
+      "inputs": {
+        "nixpkgs": [
+          "flaky",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1720042825,
+        "narHash": "sha256-A0vrUB6x82/jvf17qPCpxaM+ulJnD8YZwH9Ci0BsAzE=",
+        "owner": "nix-community",
+        "repo": "home-manager",
+        "rev": "e1391fb22e18a36f57e6999c7a9f966dc80ac073",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "ref": "release-24.05",
+        "repo": "home-manager",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1724013388,
+        "narHash": "sha256-vAq+I0IWsIDq5RUc01t25iL46LLxdsmlTJ96A30bMEY=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "3f38e71a8e23a27569acbbfee0e83b76c86fa569",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "release-24.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-22_11": {
+      "locked": {
+        "lastModified": 1688392541,
+        "narHash": "sha256-lHrKvEkCPTUO+7tPfjIcb7Trk6k31rz18vkyqmkeJfY=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "ea4c80b39be4c09702b0cb3b42eab59e2ba4f24b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "release-22.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-23_05": {
+      "locked": {
+        "lastModified": 1705957679,
+        "narHash": "sha256-Q8LJaVZGJ9wo33wBafvZSzapYsjOaNjP/pOnSiKVGHY=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "9a333eaa80901efe01df07eade2c16d183761fa3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "release-23.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-23_11": {
+      "locked": {
+        "lastModified": 1720535198,
+        "narHash": "sha256-zwVvxrdIzralnSbcpghA92tWu2DV2lwv89xZc8MTrbg=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "205fd4226592cc83fd4c0885a3e4c9c400efabb5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "release-23.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-unstable": {
+      "locked": {
+        "lastModified": 1722141560,
+        "narHash": "sha256-Ul3rIdesWaiW56PS/Ak3UlJdkwBrD4UcagCmXZR9Z7Y=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "038fb464fcfa79b4f08131b07f2d8c9a6bcc4160",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "project-manager": {
+      "inputs": {
+        "bash-strict-mode": [
+          "flaky",
+          "project-manager",
+          "flaky",
+          "bash-strict-mode"
+        ],
+        "flake-schemas": "flake-schemas",
+        "flake-utils": [
+          "flaky",
+          "project-manager",
+          "flaky",
+          "flake-utils"
+        ],
+        "flaky": [
+          "flaky"
+        ],
+        "nixpkgs": [
+          "flaky",
+          "project-manager",
+          "flaky",
+          "nixpkgs"
+        ],
+        "nixpkgs-22_11": "nixpkgs-22_11",
+        "nixpkgs-23_05": "nixpkgs-23_05",
+        "nixpkgs-23_11": "nixpkgs-23_11",
+        "nixpkgs-unstable": "nixpkgs-unstable",
+        "treefmt-nix": "treefmt-nix"
+      },
+      "locked": {
+        "lastModified": 1723360458,
+        "narHash": "sha256-l+junhIWTsYvVVFp/0YYfFPmTxODWJ2IoHesIvly4FQ=",
+        "owner": "sellout",
+        "repo": "project-manager",
+        "rev": "342359f930e23ff26a6ccdace93089f4a7fff00c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "sellout",
+        "repo": "project-manager",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "bash-strict-mode": [
+          "flaky",
+          "bash-strict-mode"
+        ],
+        "flake-utils": [
+          "flaky",
+          "flake-utils"
+        ],
+        "flaky": "flaky",
+        "nixpkgs": [
+          "flaky",
+          "nixpkgs"
+        ],
+        "systems": [
+          "flaky",
+          "systems"
+        ]
+      }
+    },
+    "shellcheck-nix-attributes": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1586929030,
+        "narHash": "sha256-a0WyWaz+nMYFWI43Ip9EUnPuBW0O4EIiTzYZKGqNjss=",
+        "owner": "Fuuzetsu",
+        "repo": "shellcheck-nix-attributes",
+        "rev": "51b49d5fe65ece69eb5e2003396bf096083ec281",
+        "type": "github"
+      },
+      "original": {
+        "owner": "Fuuzetsu",
+        "repo": "shellcheck-nix-attributes",
+        "type": "github"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1726558681,
+        "narHash": "sha256-vta8mxLa5XxpHfb9HCiavFqBrX2xJDvZiKHZOy4kvlA=",
+        "owner": "sellout",
+        "repo": "nix-systems",
+        "rev": "aa9520a9a0f92098d3576c3b4eafcb32c13d6800",
+        "type": "github"
+      },
+      "original": {
+        "owner": "sellout",
+        "repo": "nix-systems",
+        "type": "github"
+      }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "flaky",
+          "project-manager",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1722330636,
+        "narHash": "sha256-uru7JzOa33YlSRwf9sfXpJG+UAV+bnBEYMjrzKrQZFw=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "768acdb06968e53aa1ee8de207fd955335c754b7",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..b8d3820
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,117 @@
+{
+  description = "Automatically sets the dark-mode theme based on macOS/Linux/Windows status";
+
+  nixConfig = {
+    ## https://github.com/NixOS/rfcs/blob/master/rfcs/0045-deprecate-url-syntax.md
+    extra-experimental-features = ["no-url-literals"];
+    extra-substituters = ["https://cache.garnix.io"];
+    extra-trusted-public-keys = [
+      "cache.garnix.io:CTFPyKSLcx5RMJKfLo5EEPUObbA78b0YQ2DTCJXqr9g="
+    ];
+    ## Isolate the build.
+    sandbox = "relaxed";
+    use-registries = false;
+  };
+
+  outputs = {
+    bash-strict-mode,
+    flake-utils,
+    flaky,
+    nixpkgs,
+    self,
+    systems,
+  }: let
+    pname = "auto-dark";
+
+    supportedSystems = import systems;
+  in
+    {
+      schemas = {
+        inherit
+          (flaky.schemas)
+          overlays
+          homeConfigurations
+          packages
+          devShells
+          checks
+          formatter
+          ;
+      };
+
+      overlays = {
+        default = flaky.lib.elisp.overlays.default self.overlays.emacs;
+
+        emacs = final: prev: efinal: eprev: {inherit (self.packages.${final.system}) auto-dark;};
+      };
+
+      homeConfigurations =
+        builtins.listToAttrs
+        (builtins.map
+          (flaky.lib.homeConfigurations.example self [./example/home.nix])
+          supportedSystems);
+    }
+    // flake-utils.lib.eachSystem supportedSystems (system: let
+      pkgs = nixpkgs.legacyPackages.${system}.appendOverlays [
+        flaky.overlays.dependencies
+        flaky.overlays.elisp-dependencies
+      ];
+
+      src = pkgs.lib.cleanSource ./.;
+    in {
+      packages =
+        {
+          default = self.packages.${system}.auto-dark;
+          auto-dark = pkgs.callPackage ./nix/packages/auto-dark.nix {
+            inherit src;
+            inherit (pkgs) emacsPackages;
+            checkedDrv = bash-strict-mode.lib.checkedDrv pkgs;
+          };
+        }
+        // nixpkgs.lib.listToAttrs (nixpkgs.lib.concatMap (v:
+          if nixpkgs.lib.elem system pkgs.${v}.meta.platforms
+          then [
+            {
+              name = "${v}_auto-dark";
+              value = pkgs.callPackage ./nix/packages/auto-dark.nix {
+                inherit src;
+                checkedDrv = bash-strict-mode.lib.checkedDrv pkgs;
+                emacsPackages = pkgs.emacsPackagesFor pkgs.${v};
+              };
+            }
+          ]
+          else []) [
+          ## Emacs 28 doesn’t like setting up frames in batch mode, so only test
+          ## on Emacs 29 for now.
+          "emacs29"
+          "emacs29-gtk3"
+          "emacs29-macport"
+          "emacs29-nox"
+          "emacs29-pgtk"
+        ]);
+
+      devShells.default = bash-strict-mode.lib.checkedDrv pkgs (pkgs.mkShell {
+        inherit (pkgs) system;
+        inputsFrom =
+          builtins.attrValues self.checks.${system}
+          ++ builtins.attrValues self.packages.${system};
+      });
+
+      checks = import ./nix/checks.nix {
+        inherit src;
+        inherit (pkgs) emacsPackages emacsWithPackages stdenv;
+        checkedDrv = bash-strict-mode.lib.checkedDrv pkgs;
+      };
+
+      formatter = pkgs.alejandra;
+    });
+
+  inputs = {
+    ## Flaky should generally be the source of truth for its inputs.
+    flaky.url = "github:sellout/flaky";
+
+    bash-strict-mode.follows = "flaky/bash-strict-mode";
+    flake-utils.follows = "flaky/flake-utils";
+    nixpkgs.follows = "flaky/nixpkgs";
+    systems.follows = "flaky/systems";
+  };
+}
diff --git a/garnix.yaml b/garnix.yaml
new file mode 100644
index 0000000..9d550af
--- /dev/null
+++ b/garnix.yaml
@@ -0,0 +1,13 @@
+{
+    "builds": {
+        "exclude": [
+            "*.x86_64-darwin",
+            "*.x86_64-darwin.*",
+            "homeConfigurations.x86_64-darwin-example"
+        ],
+        "include": [
+            "*.*",
+            "*.*.*"
+        ]
+    }
+}
diff --git a/initialize/auto-dark-initialize.el b/initialize/auto-dark-initialize.el
new file mode 100644
index 0000000..97acf7b
--- /dev/null
+++ b/initialize/auto-dark-initialize.el
@@ -0,0 +1,60 @@
+;;; auto-dark-initialize.el --- Functions to simulate Emacs’ initialization  -*- lexical-binding: t; -*-
+
+;; Author: Greg Pfeil <greg@technomadic.org>
+;; Created: October 11 2024
+;; Version: 0.1.0
+;; Keywords: maint, tools
+;; URL: https://github.com/LionyxML/auto-dark-emacs
+;; SPDX-License-Identifier: AGPL-3.0-or-later
+
+;;; Commentary:
+
+;; This library attempts to simulate the Emacs initialization process, for
+;; writing tests that are sensitive to initialization.
+
+;;; Code:
+
+(defvar auto-dark-initialize--current-state nil
+  "The phase of initialization we’ve gotten to.
+So users don’t have to call every function.")
+
+(defun auto-dark-initialize-start ()
+  "Set up various things to a state similar to what existed before early init."
+  (if auto-dark-initialize--current-state
+      (lwarn 'auto-dark-initialize :warn
+             "Initialization is already at least as far as 'start, not running.")
+    (setq after-init-time nil
+          auto-dark-initialize--current-state 'start)))
+
+(defun auto-dark-initialize-after-early-init (autoload-features)
+  "Update state as done between early init and the rest of the init files.
+E.g., initializing the package system and setting up the display.
+AUTOLOAD-FEATURES should be a list of symbols naming the autoload features for
+packages you are testing."
+  (unless auto-dark-initialize--current-state
+    (auto-dark-initialize-start))
+  (if (eq auto-dark-initialize--current-state 'start)
+      (progn
+        (mapc (lambda (feature) (require feature)) autoload-features)
+        (custom-set-variables
+         '(frame-background-mode 'light))
+        (setq auto-dark-initialize--current-state 'early-init))
+    (lwarn 'auto-dark-initialize :warn
+           "Initialization is already at least as far as 'early-init, not running.")))
+
+(defun auto-dark-initialize-finish ()
+  "This is the rest of the init process after the various files are loaded.
+After this is run, the tests should reflect a “normal” Emacs session."
+  (pcase auto-dark-initialize--current-state
+    ('(nil start)
+     (signal 'auto-dark-initialize
+             '("At least ‘auto-dark-initialize-after-early-init needs to be called first.’")))
+    ('early-init
+     (setq after-init-time (current-time))
+     (run-hooks 'after-init-hook)
+     (setq auto-dark-initialize--current-state 'finished))
+    (_ (lwarn 'auto-dark-initialize :warn
+              "Initialization has already finished, not running."))))
+
+(provide 'auto-dark-initialize)
+;;; auto-dark-initialize.el ends here
diff --git a/nix/checks.nix b/nix/checks.nix
new file mode 100644
index 0000000..5f11d05
--- /dev/null
+++ b/nix/checks.nix
@@ -0,0 +1,81 @@
+{
+  checkedDrv,
+  emacsPackages,
+  emacsWithPackages,
+  src,
+  stdenv,
+}: let
+  lib = import ./lib.nix {inherit emacsPackages;};
+in {
+  doctor = checkedDrv (stdenv.mkDerivation {
+    inherit src;
+    inherit (lib) ELDEV_LOCAL;
+
+    name = "eldev doctor";
+
+    nativeBuildInputs = [
+      (emacsWithPackages (e: [e.elisp-lint]))
+      # Emacs-lisp build tool, https://doublep.github.io/eldev/
+      emacsPackages.eldev
+    ];
+
+    buildPhase = ''
+      runHook preBuild
+      ## TODO: Currently needed to make a temp file in
+      ##      `eldev--create-internal-pseudoarchive-descriptor`.
+      HOME="$(mktemp --directory --tmpdir fake-home.XXXXXX)"
+      mkdir -p "$HOME/.cache/eldev"
+      ## NB: `EMACSNATIVELOADPATH` is needed by `elisp-lin
+      EMACSNATIVELOADPATH= eldev doctor
+      runHook postBuild
+    '';
+
+    installPhase = ''
+      runHook preInstall
+      mkdir -p "$out"
+      runHook postInstall
+    '';
+  });
+
+  lint = let
+    emacs = emacsWithPackages (e: [
+      e.elisp-lint
+      e.package-lint
+      e.relint
+    ]);
+  in
+    checkedDrv (stdenv.mkDerivation {
+      inherit src;
+      inherit (lib) ELDEV_LOCAL;
+
+      name = "eldev lint";
+
+      nativeBuildInputs = [
+        emacs
+        emacsPackages.eldev
+      ];
+
+      postPatch = lib.setUpLocalDependencies emacs.deps;
+
+      buildPhase = ''
+        runHook preBuild
+
+        ## Need `--external` here so that we don’t try to download any
+        ## package archives (which would break the sandbox).
+        ## NB: `EMACSNATIVELOADPATH` is needed by `elisp-lint`.
+        ## TODO: Currently need `HOME` to make a temp file in
+        ##      `eldev--create-internal-pseudoarchive-descriptor`.
+        EMACSNATIVELOADPATH= \
+          HOME="$(mktemp --directory --tmpdir fake-home.XXXXXX)" \
+          eldev --external lint --required
+
+        runHook postBuild
+      '';
+
+      installPhase = ''
+        runHook preInstall
+        mkdir -p "$out"
+        runHook preInstall
+      '';
+    });
+}
diff --git a/nix/lib.nix b/nix/lib.nix
new file mode 100644
index 0000000..e6e588b
--- /dev/null
+++ b/nix/lib.nix
@@ -0,0 +1,21 @@
+{emacsPackages}: let
+  emacsPath = package: "${package}/share/emacs/site-lisp/elpa/${package.pname}-${package.version}";
+in {
+  ## We need to tell Eldev where to find its Emacs package.
+  ELDEV_LOCAL = emacsPath emacsPackages.eldev;
+
+  ## Ideally this could just
+  ##     (setq eldev-external-package-dir "${deps}/share/emacs/site-lisp/elpa")
+  ## but Eldev wants to write to that directory, even if there's nothing to
+  ## download.
+  setUpLocalDependencies = deps: ''
+    {
+      echo
+      echo "(mapcar 'eldev-use-local-dependency"
+      echo "        (directory-files"
+      echo "         \"${deps}/share/emacs/site-lisp/elpa\""
+      echo "         t"
+      echo "         directory-files-no-dot-files-regexp))"
+    } >> Eldev
+  '';
+}
diff --git a/nix/packages/auto-dark.nix b/nix/packages/auto-dark.nix
new file mode 100644
index 0000000..1a20952
--- /dev/null
+++ b/nix/packages/auto-dark.nix
@@ -0,0 +1,81 @@
+{
+  checkedDrv,
+  emacsPackages,
+  src,
+}: let
+  lib = import ../lib.nix {inherit emacsPackages;};
+
+  ## Read version in format: ;; Version: x.y(.z)?
+  readVersion = fp:
+    builtins.elemAt
+    (builtins.match
+      ".*(;; Version: ([[:digit:]]+\.[[:digit:]]+(\.[[:digit:]]+)?)).*"
+      (builtins.readFile fp))
+    1;
+
+  emacsWithPackages = emacsPackages.emacsWithPackages (epkgs: [
+    epkgs.buttercup
+    epkgs.elisp-lint
+    epkgs.use-package # TODO: Conditionalize on Emacs <29?
+  ]);
+in
+  checkedDrv (emacsPackages.trivialBuild {
+    inherit src;
+    inherit (lib) ELDEV_LOCAL;
+
+    pname = "auto-dark";
+
+    version = readVersion ../../auto-dark.el;
+
+    nativeBuildInputs = [
+      emacsWithPackages
+      # Emacs-lisp build tool, https://doublep.github.io/eldev/
+      emacsPackages.eldev
+    ];
+
+    postPatch = lib.setUpLocalDependencies emacsWithPackages.deps;
+
+    doCheck = true;
+
+    checkPhase = ''
+      runHook preCheck
+
+      ## TODO: Currently needed to make a temp file in
+      ##      `eldev--create-internal-pseudoarchive-descriptor`.
+      HOME="$(mktemp --directory --tmpdir fake-home.XXXXXX)"
+
+      ## Need `--external` here so that we don’t try to download any
+      ## package archives (which would break the sandbox).
+      eldev --external test --test-type=main
+
+      runHook postCheck
+    '';
+
+    doInstallCheck = true;
+
+    installCheckPhase = ''
+      runHook preInstallCheck
+
+      init_tests=($(IFS=$'\n' find ./tests/initialization -type f -name '*.el'))
+      # This tries to make sure we don’t have a bug that skips the tests.
+      if (( ''${#init_tests[@]} == 0 )); then
+        echo "didn’t find initialization tests" >2
+        exit 1
+      else
+        for file in "''${init_tests[@]}"; do
+          echo "testing $file"
+          eldev --external test --test-type=integration -f "$file"
+        done
+      fi
+
+      ## TODO: Currently needed to make a temp file in
+      ##      `eldev--create-internal-pseudoarchive-descriptor`.
+      HOME="$(mktemp --directory --tmpdir fake-home.XXXXXX)"
+
+      ## Need `--external` here so that we don’t try to download any
+      ## package archives (which would break the sandbox).
+      eldev --external --packaged test --test-type=main
+
+      runHook postInstallCheck
+    '';
+  })
diff --git a/tests/basic.el b/tests/basic.el
new file mode 100644
index 0000000..57df10f
--- /dev/null
+++ b/tests/basic.el
@@ -0,0 +1,62 @@
+;;; basic.el --- Tests that work in any environment -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+(require 'auto-dark)
+(require 'buttercup)
+
+;; Track whether `auto-dark-mode' was enabled before we started the tests.
+(defvar auto-dark-tests--original-state auto-dark-mode)
+(defvar auto-dark-tests--original-enabled-themes custom-enabled-themes)
+
+(custom-set-variables
+ ;; TODO: This is not a valid value, but it stops Auto-Dark from trying to set
+ ;;       the detection method. See #73.
+ '(auto-dark-detection-method 'manual)
+ '(custom-enabled-themes ())
+ '(frame-background-mode 'light))
+
+;; Ensure `auto-dark-mode' is disabled for this part of the test.
+(when auto-dark-tests--original-state
+  (auto-dark-mode -1))
+
+(describe "when disabled"
+  (it "shouldn’t affect enabled themes"
+    (expect custom-enabled-themes :to-be nil)
+    (custom-set-variables
+     '(auto-dark-themes '((tango-dark) (tango))))
+    (expect auto-dark-themes :to-equal '((tango-dark) (tango)))
+    (expect custom-enabled-themes :to-be nil)))
+
+(describe "when enabled"
+  (it "should immediately update themes"
+    (expect auto-dark-themes :to-equal '((tango-dark) (tango)))
+    (auto-dark-mode 1)
+    (expect auto-dark-themes :to-equal '((tango-dark) (tango)))
+    (expect custom-enabled-themes :to-equal '(tango)))
+  (it "should reflect changes to themes immediately"
+    (custom-set-variables
+     '(auto-dark-themes '((wombat) (leuven))))
+    (expect auto-dark-themes :to-equal '((wombat) (leuven)))
+    (expect custom-enabled-themes :to-equal '(leuven))))
+
+(describe "toggling"
+  (before-each
+    (auto-dark-toggle-appearance))
+  (it "should invert the current appearance"
+    (expect custom-enabled-themes :to-equal '(wombat)))
+  (it "should invert the current appearance again"
+    (expect custom-enabled-themes :to-equal '(leuven)))
+  (it "should invert the current appearance and again"
+    (expect custom-enabled-themes :to-equal '(wombat))))
+
+;; Restore the original state
+(unless auto-dark-tests--original-state
+  (auto-dark-mode -1))
+
+(custom-set-variables
+ '(custom-enabled-themes auto-dark-tests--original-enabled-themes))
+
+;;; basic.el ends here
diff --git a/tests/initialization/README.md b/tests/initialization/README.md
new file mode 100644
index 0000000..ae25789
--- /dev/null
+++ b/tests/initialization/README.md
@@ -0,0 +1,5 @@
+# initialization tests
+
+These files test that the package behaves in various contexts when first loaded.
+
+They each need to be run in their own instance, to ensure they don’t interfere with each other.
diff --git a/tests/initialization/customize-first.el b/tests/initialization/customize-first.el
new file mode 100644
index 0000000..c344083
--- /dev/null
+++ b/tests/initialization/customize-first.el
@@ -0,0 +1,60 @@
+;;; customize-first.el --- Customize vars before enabling -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; Tests the recommended flow of customizing variables before enabling
+;; Auto-Dark.
+
+;;; Code:
+
+(require 'auto-dark-initialize)
+(require 'buttercup)
+
+(describe "package initialization with variables pre-set"
+  (before-all
+    (auto-dark-initialize-after-early-init '(auto-dark-autoloads))
+    (custom-set-variables
+     '(auto-dark-themes '((tsdh-dark) (tsdh-light)))))
+  (describe "before enabling"
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "after enabling"
+    (before-all
+      (auto-dark-mode 1))
+    (it "themes should be enabled"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light))))
+    (it "should have bound Auto-Dark variables"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)))
+
+  (describe "after init"
+    (before-all
+      (auto-dark-initialize-finish))
+    (it "themes should be enabled"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light))))
+    (it "Old Auto-Dark variables should now be set"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      (expect auto-dark-dark-theme :to-be 'wombat)
+      (expect auto-dark-light-theme :to-be 'leuven))))
+
+;;; customize-first.el ends here
diff --git a/tests/initialization/de-facto-old.el b/tests/initialization/de-facto-old.el
new file mode 100644
index 0000000..4f0c7f1
--- /dev/null
+++ b/tests/initialization/de-facto-old.el
@@ -0,0 +1,84 @@
+;;; de-facto-old.el --- Tests that need to be run in a fresh instance -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; This models the most common initialization style of Emacs, where Customize
+;; inserts a `custom-set-variables' form at the end of `user-init-file'.
+
+;; 1. `package-initialize' is called, then
+;; 2. `user-init-file' is loaded, which has
+;;   a. some initialization of `auto-dark-mode' and
+;;   b. `custom-set-variables' at the end.
+
+;;; Code:
+
+(require 'auto-dark-initialize)
+(require 'buttercup)
+
+;; To silence “reference to free variable” warnings
+(defvar auto-dark-allow-osascript)
+(defvar auto-dark-allow-powershell)
+(defvar auto-dark-dark-theme)
+(defvar auto-dark-light-theme)
+(defvar auto-dark-polling-interval-seconds)
+(defvar auto-dark-themes)
+
+(describe "Emacs’s de-facto initialization with old theme vars"
+  (before-all
+    (auto-dark-initialize-after-early-init '(auto-dark-autoloads)))
+
+  (describe "after ‘package-initialize’ is called"
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "before ‘custom-set-variables’ is called"
+    (before-all
+      (auto-dark-mode 1))
+
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-equal ()))
+    (it "should have bound Auto-Dark variables to their standard values"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-be nil)
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)))
+
+  (describe "after vars are set"
+    (before-all
+      (custom-set-variables
+       '(auto-dark-dark-theme 'tsdh-dark)
+       '(auto-dark-light-theme 'tsdh-light)))
+
+    ;; NB: When using the old variables, they won’t be set until
+    ;;    `after-init-hook' is run.
+    (it "shouldn’t have changed anything yet"
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)))
+
+  (describe "after ‘user-init-file’ is loaded"
+    (before-all
+      (auto-dark-initialize-finish))
+
+    (it "should have configured Auto-Dark"
+      (expect auto-dark-themes :to-be nil)
+      ;; And _now_ these have their standard values.
+      (expect auto-dark-dark-theme :to-be 'tsdh-dark)
+      (expect auto-dark-light-theme :to-be 'tsdh-light))
+
+    (it "should have enabled the correct themes"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light))))))
+
+;;; de-facto-old.el ends here
diff --git a/tests/initialization/de-facto.el b/tests/initialization/de-facto.el
new file mode 100644
index 0000000..b4f7078
--- /dev/null
+++ b/tests/initialization/de-facto.el
@@ -0,0 +1,74 @@
+;;; de-facto.el --- Tests that need to be run in a fresh instance -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; This models the most common initialization style of Emacs, where Customize
+;; inserts a `custom-set-variables' form at the end of `user-init-file'.
+
+;; 1. `package-initialize' is called, then
+;; 2. `user-init-file' is loaded, which has
+;;   a. some initialization of `auto-dark-mode' and
+;;   b. `custom-set-variables' at the end.
+
+;;; Code:
+
+(require 'auto-dark-initialize)
+(require 'buttercup)
+
+;; To silence “reference to free variable” warnings
+(defvar auto-dark-allow-osascript)
+(defvar auto-dark-allow-powershell)
+(defvar auto-dark-dark-theme)
+(defvar auto-dark-detection-method)
+(defvar auto-dark-light-theme)
+(defvar auto-dark-polling-interval-seconds)
+(defvar auto-dark-themes)
+
+(describe "Emacs’s de-facto initialization"
+  (before-all
+    (auto-dark-initialize-after-early-init '(auto-dark-autoloads)))
+
+  (describe "after ‘package-initialize’ is called"
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "before ‘custom-set-variables’ is called"
+    (before-all
+      (auto-dark-mode 1))
+
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-equal ()))
+    (it "should have bound Auto-Dark variables to their standard values"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-be nil)
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)))
+
+  (describe "after variables are set"
+    (before-all
+      (custom-set-variables
+       '(auto-dark-themes '((tsdh-dark) (tsdh-light)))))
+
+    (it "should have configured Auto-Dark"
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      ;; And these are still unbound.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil))
+
+    (it "should have enabled the correct themes"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light))))))
+
+;;; de-facto.el ends here
diff --git a/tests/initialization/defaults.el b/tests/initialization/defaults.el
new file mode 100644
index 0000000..35d0c28
--- /dev/null
+++ b/tests/initialization/defaults.el
@@ -0,0 +1,73 @@
+;;; defaults.el --- Tests that need to be run in a fresh instance -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; This models the most common initialization style of Emacs, where Customize
+;; inserts a `custom-set-variables' form at the end of `user-init-file'.
+
+;; 1. `package-initialize' is called, then
+;; 2. `user-init-file' is loaded, which has
+;;   a. some initialization of `auto-dark-mode' and
+;;   b. `custom-set-variables' at the end.
+
+;;; Code:
+
+(require 'auto-dark-initialize)
+(require 'buttercup)
+
+;; To silence “reference to free variable” warnings
+(defvar auto-dark-allow-osascript)
+(defvar auto-dark-allow-powershell)
+(defvar auto-dark-dark-theme)
+(defvar auto-dark-detection-method)
+(defvar auto-dark-light-theme)
+(defvar auto-dark-polling-interval-seconds)
+(defvar auto-dark-themes)
+
+(describe "Emacs’s de-facto initialization with old theme vars"
+  (before-all
+    (auto-dark-initialize-after-early-init '(auto-dark-autoloads)))
+
+  (describe "after ‘package-initialize’ is called"
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "before ‘custom-set-variables’ is called"
+    (before-all
+      (auto-dark-mode 1))
+
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-equal ()))
+    (it "should have bound Auto-Dark variables to their standard values"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-be nil)
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)))
+
+  (describe "after ‘user-init-file’ is loaded"
+    (before-all
+      (auto-dark-initialize-finish))
+
+    (it "should have configured Auto-Dark"
+      (expect auto-dark-themes :to-be nil)
+      ;; And _now_ these have their standard values.
+      (expect auto-dark-dark-theme :to-be 'wombat)
+      (expect auto-dark-light-theme :to-be 'leuven))
+
+    (it "should have enabled the correct themes"
+      (expect custom-enabled-themes :to-be-in '((wombat) (leuven))))))
+
+;;; defaults.el ends here
diff --git a/tests/initialization/early-init.el b/tests/initialization/early-init.el
new file mode 100644
index 0000000..b8ca914
--- /dev/null
+++ b/tests/initialization/early-init.el
@@ -0,0 +1,82 @@
+;;; early-init.el --- Customize in early-init -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; This is more of an edge case, but it customizes the variables in early init,
+;; and then enables the package in regular init.
+
+;;; Code:
+
+(require 'auto-dark-initialize)
+(require 'buttercup)
+
+;; To silence “reference to free variable” warnings
+(defvar auto-dark-themes)
+
+(describe "customization in early init"
+  (before-all
+    (auto-dark-initialize-start)
+    (custom-set-variables
+     '(auto-dark-themes '((tsdh-dark) (tsdh-light)))))
+
+  (describe "in early init"
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ())
+      (expect (boundp 'auto-dark-themes) :to-be nil))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "after early init"
+    (before-all
+      (auto-dark-initialize-after-early-init '(auto-dark-autoloads)))
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "after package is loaded"
+    (before-all
+      (require 'auto-dark))
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should have bound Auto-Dark variables"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)))
+
+  ;; FIXME: Make sure this is always in a particular mode, or check for either set.
+  (describe "after-enabling"
+    (before-all
+      (auto-dark-mode 1))
+    (it "themes should be enabled"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light))))
+    (it "Auto-Dark variables should be unchanged"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil))))
+
+;;; early-init.el ends here
diff --git a/tests/initialization/use-package-config.el b/tests/initialization/use-package-config.el
new file mode 100644
index 0000000..cad992b
--- /dev/null
+++ b/tests/initialization/use-package-config.el
@@ -0,0 +1,62 @@
+;;; use-package-config.el --- Use-package with :config -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; This tests a common `use-package' style of initialization.
+
+;;; Code:
+
+(require 'auto-dark-initialize)
+(require 'buttercup)
+
+(describe "‘use-package’ initialization with :config"
+  (before-all
+    (auto-dark-initialize-after-early-init '(auto-dark-autoloads)))
+
+  (describe "after ‘package-initialize’ is called"
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "after ‘user-init-file’ is loaded"
+    (before-all
+      (use-package auto-dark
+        :custom (auto-dark-themes '((tsdh-dark) (tsdh-light)))
+        :config (auto-dark-mode)))
+
+    (it "should have configured Auto-Dark"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil))
+    (it "should have enabled the themes"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light)))))
+
+  (describe "after init"
+    (before-all
+      (auto-dark-initialize-finish))
+
+    (it "should have configured Auto-Dark"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      (expect auto-dark-dark-theme :to-be 'wombat)
+      (expect auto-dark-light-theme :to-be 'leuven))
+    (it "should have enabled the themes"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light))))))
+
+;;; use-package-config.el ends here
diff --git a/tests/initialization/use-package-init.el b/tests/initialization/use-package-init.el
new file mode 100644
index 0000000..1197de8
--- /dev/null
+++ b/tests/initialization/use-package-init.el
@@ -0,0 +1,55 @@
+;;; use-package-init.el --- Use-package with :init -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; This tests a common `use-package' style of initialization.
+
+;;; Code:
+
+(require 'auto-dark-initialize)
+(require 'buttercup)
+
+;; To silence “reference to free variable” warnings
+(defvar auto-dark-allow-osascript)
+(defvar auto-dark-allow-powershell)
+(defvar auto-dark-dark-theme)
+(defvar auto-dark-light-theme)
+(defvar auto-dark-polling-interval-seconds)
+(defvar auto-dark-themes)
+
+(describe "‘use-package’ initialization with :init"
+  (before-all
+    (auto-dark-initialize-after-early-init '(auto-dark-autoloads)))
+
+  (describe "after ‘package-initialize’ is called"
+    (it "should not have enabled the themes yet"
+      (expect custom-enabled-themes :to-be ()))
+    (it "should not have bound Auto-Dark variables"
+      (expect (boundp 'auto-dark-allow-osascript) :to-be nil)
+      (expect (boundp 'auto-dark-allow-powershell) :to-be nil)
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil)
+      (expect (boundp 'auto-dark-polling-interval-seconds) :to-be nil)
+      (expect (boundp 'auto-dark-themes) :to-be nil)))
+
+  (describe "after ‘user-init-file’ is loaded"
+    (before-all
+      (use-package auto-dark
+        :custom (auto-dark-themes '((tsdh-dark) (tsdh-light)))
+        :config (auto-dark-mode)))
+
+    (it "should have configured Auto-Dark"
+      (expect auto-dark-allow-osascript :to-be nil)
+      (expect auto-dark-allow-powershell :to-be nil)
+      (expect (boundp 'auto-dark-detection-method) :to-be-truthy)
+      (expect auto-dark-polling-interval-seconds :to-be 5)
+      (expect auto-dark-themes :to-equal '((tsdh-dark) (tsdh-light)))
+      ;; These two are handled specially – they aren’t set to their defaults
+      ;; until after initialization.
+      (expect (boundp 'auto-dark-dark-theme) :to-be nil)
+      (expect (boundp 'auto-dark-light-theme) :to-be nil))
+    (it "should have enabled the themes"
+      (expect custom-enabled-themes :to-be-in '((tsdh-dark) (tsdh-light))))))
+
+;;; use-package-init.el ends here