Add test suite and fix failing tests

.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 . 167)
+  (indent-tabs-mode . nil)
+  (sentence-end-double-space . nil)))

.envrc

@@ -0,0 +1,2 @@
+direnv_layout_dir="$PWD/.cache/direnv"
+use flake

.github/renovate.json

@@ -0,0 +1,10 @@
+{
+    "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+    "extends": ["config:base"],
+    "lockFileMaintenance": {
+        "enabled":true
+    },
+    "nix": {
+        "enabled":true
+    }
+}

.gitignore

@@ -1 +1,5 @@
-*.DS_Store
+*.elc
+/.cache/direnv/
+/dist
+/.eldev
+/result

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"))