diff --git a/src/stk/_internal/building_block.py b/src/stk/_internal/building_block.py
index f3f01f160..f5a25cffc 100644
--- a/src/stk/_internal/building_block.py
+++ b/src/stk/_internal/building_block.py
@@ -782,6 +782,7 @@ def _with_functional_groups(
         """
 
         self._functional_groups = tuple(functional_groups)
+        self._fg_repr = repr(self._functional_groups)
         return self
 
     def with_functional_groups(
@@ -812,6 +813,7 @@ def _with_canonical_atom_ordering(self) -> typing.Self:
             functional_group.with_ids(id_map)
             for functional_group in self._functional_groups
         )
+        self._fg_repr = repr(self._functional_groups)
         self._placer_ids = frozenset(
             id_map[placer_id] for placer_id in self._placer_ids
         )
diff --git a/src/stk/_internal/topology_graphs/host_guest/complex.py b/src/stk/_internal/topology_graphs/host_guest/complex.py
index 15669d4f8..f692ebd42 100644
--- a/src/stk/_internal/topology_graphs/host_guest/complex.py
+++ b/src/stk/_internal/topology_graphs/host_guest/complex.py
@@ -37,7 +37,7 @@ def __init__(
         building_block: BuildingBlock,
         start_vector: tuple[float, float, float] = (1.0, 0.0, 0.0),
         end_vector: tuple[float, float, float] = (1.0, 0.0, 0.0),
-        displacement: tuple[float, float, float] = (1.0, 0.0, 0.0),
+        displacement: tuple[float, float, float] = (0.0, 0.0, 0.0),
     ) -> None:
         """
         Initialize a :class:`.Guest` instance.
@@ -410,7 +410,7 @@ class Complex(TopologyGraph):
         *Changing the Position of the Guest*
 
         You can change the position and orientation of the
-        :class:`.Guest`, as well as its displacement
+        :class:`.Guest`.
 
         .. testcode:: changing-the-position-of-the-guest
 
@@ -449,6 +449,13 @@ class Complex(TopologyGraph):
                 ),
             )
 
+    .. tip::
+
+        The host of a :class:`.Complex` will always be placed at the
+        origin, not at the centroid of the input building block. Therefore,
+        to place a guest at the centroid of the host use
+        `displacement=(0, 0, 0)`, which is the default behaviour.
+
     """
 
     def __init__(
@@ -521,7 +528,7 @@ def _get_vertices_from_guests(
                         target=guest.get_end_vector(),
                     ),
                 ]
-        return building_block_vertices  # type: ignore
+        return building_block_vertices  # type: ignore[return-value]
 
     def clone(self) -> Complex:
         return self._clone()
diff --git a/src/stk/_internal/writers/turbomole.py b/src/stk/_internal/writers/turbomole.py
index a26dcacf2..22aeb9406 100644
--- a/src/stk/_internal/writers/turbomole.py
+++ b/src/stk/_internal/writers/turbomole.py
@@ -1,9 +1,3 @@
-"""
-Turbomole Writer
-================
-
-"""
-
 from __future__ import annotations
 
 import typing
@@ -11,6 +5,7 @@
 from stk._internal.molecule import Molecule
 from stk._internal.periodic_info import PeriodicInfo
 from stk._internal.utilities.utilities import OneOrMany
+import pathlib
 
 
 class TurbomoleWriter:
@@ -144,7 +139,7 @@ def to_string(
     def write(
         self,
         molecule: Molecule,
-        path: str,
+        path: pathlib.Path | str,
         atom_ids: typing.Optional[OneOrMany[int]] = None,
         periodic_info: typing.Optional[PeriodicInfo] = None,
     ) -> None:
diff --git a/tests/molecular/molecules/building_block/case_data.py b/tests/molecular/molecules/building_block/case_data.py
index 0fb4a3a44..094c39b1f 100644
--- a/tests/molecular/molecules/building_block/case_data.py
+++ b/tests/molecular/molecules/building_block/case_data.py
@@ -1,59 +1,12 @@
-class CaseData:
-    """
-    A test case.
-
-    Attributes
-    ----------
-    building_block : :class:`.BuildingBlock`
-        The building block to test.
-
-    functional_groups : :class:`tuple` of :class:`.FunctionalGroup`
-        The functional groups :attr:`.building_block` should be
-        holding.
-
-    known_repr : str
-        The representation of the building block.
-
-    core_atom_ids : :class:`tuple` of :class:`int`
-        The correct core atom ids for :attr:`.building_block`.
-
-    placer_ids : :class:`tuple` of :class:`int`
-        The correct *placer* ids for :attr:`.building_block`.
-
-    """
+import stk
+from dataclasses import dataclass
+from collections.abc import Sequence
 
-    def __init__(
-        self,
-        building_block,
-        functional_groups,
-        known_repr,
-        core_atom_ids,
-        placer_ids,
-    ):
-        """
-        Initialize a :class:`.CaseData` instance.
 
-        Parameters
-        ----------
-        building_block : :class:`.BuildingBlock`
-            The building block to test.
-
-        functional_groups : :class:`tuple` of :class:`.FunctionalGroup`
-            The functional groups `building_block` should be holding.
-
-        known_repr : str
-            The representation of the building block.
-
-        core_atom_ids : :class:`tuple` of :class:`int`
-            The correct core atom ids for `building_block`.
-
-        placer_ids : :class:`tuple` of :class:`int`
-            The correct *placer* ids for `building_block`.
-
-        """
-
-        self.building_block = building_block
-        self.functional_groups = functional_groups
-        self.known_repr = known_repr
-        self.core_atom_ids = core_atom_ids
-        self.placer_ids = placer_ids
+@dataclass(slots=True, frozen=True)
+class CaseData:
+    building_block: stk.BuildingBlock
+    functional_groups: Sequence[stk.FunctionalGroup]
+    known_repr: str
+    core_atom_ids: Sequence[int]
+    placer_ids: Sequence[int]
diff --git a/tests/molecular/molecules/building_block/conftest.py b/tests/molecular/molecules/building_block/conftest.py
index bd387e265..4fe37a693 100644
--- a/tests/molecular/molecules/building_block/conftest.py
+++ b/tests/molecular/molecules/building_block/conftest.py
@@ -3,10 +3,13 @@
 import pytest
 import stk
 from pytest_lazyfixture import lazy_fixture
+from collections import abc
 
 # Fixtures need be visible for lazy_fixture() calls.
 from .fixtures import *  # noqa
 
+from .case_data import CaseData
+
 
 @pytest.fixture(
     params=(
@@ -17,7 +20,7 @@
         lazy_fixture("init_from_rdkit_mol"),
     ),
 )
-def case_data(request):
+def case_data(request) -> CaseData:
     """
     A :class:`.CaseData` instance.
 
@@ -27,7 +30,7 @@ def case_data(request):
 
 
 @pytest.fixture
-def building_block(case_data):
+def building_block(case_data: CaseData) -> stk.BuildingBlock:
     """
     A :class:`.BuildingBlock` instance.
 
@@ -48,18 +51,17 @@ def building_block(case_data):
         ),
     )
 )
-def get_functional_groups(request):
+def get_functional_groups(
+    request: pytest.FixtureRequest,
+) -> abc.Iterable[stk.FunctionalGroup]:
     """
-    Yield the functional groups of a `molecule`.
+    Get the functional groups of a `molecule`.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        The molecule whose functional groups should be gotten.
+    Parameters:
+        molecule:
+            The molecule whose functional groups should be gotten.
 
-    Yields
-    ------
-    :class:`.FunctionalGroup`
+    Returns:
         A functional group of `molecule`.
 
     """
diff --git a/tests/molecular/molecules/building_block/fixtures/init_from_file.py b/tests/molecular/molecules/building_block/fixtures/init_from_file.py
index 606d0be86..9c05409e5 100644
--- a/tests/molecular/molecules/building_block/fixtures/init_from_file.py
+++ b/tests/molecular/molecules/building_block/fixtures/init_from_file.py
@@ -1,104 +1,26 @@
 import pytest
 import stk
-
+from collections.abc import Sequence
 from ..case_data import CaseData
+from dataclasses import dataclass
 
 
 @pytest.fixture(
-    params=[
-        "building_block.mol",
-    ],
+    params=["building_block.mol"],
 )
 def path(tmpdir, request):
     return tmpdir / request.param
 
 
+@dataclass(frozen=True, slots=True)
 class InitFromFileData:
-    """
-    Stores data for the :meth:`.BuildingBlock.init_from_file`.
-
-    Attributes
-    ----------
-    building_block : :class:`.BuildingBlock`
-        The building block, which will be written to a file, so that it
-        can be initialized from it.
-
-    init_functional_groups : :class:`iterable`
-        Passed to the `functional_groups` parameter of
-        :meth:`.BuildingBlock.init_from_file`.
-
-    init_placer_ids : :class:`tuple` or :class:`NoneType`
-        Passed to the `placer_ids` parameter of
-        :meth:`.BuildingBlock.init_from_file`.
-
-    case_data_functional_groups : :class:`tuple`
-        The functional groups the initialized building block should
-        have.
-
-    case_data_core_atom_ids : :class:`tuple` of :class:`int`
-        The ids of core atoms the initialized building block should
-        have.
-
-    case_data_placer_ids : :class:`tuple` of :class:`int`
-        The ids of *placer* atoms the initialized building block should
-        have.
-
-    known_repr : str
-        The representation of the building block.
-
-    """
-
-    def __init__(
-        self,
-        building_block,
-        init_functional_groups,
-        init_placer_ids,
-        case_data_functional_groups,
-        case_data_core_atom_ids,
-        case_data_placer_ids,
-        known_repr,
-    ):
-        """
-        Initialize a :class:`.InitFromData` instance.
-
-        Parameters
-        ----------
-        building_block : :class:`.BuildingBlock`
-            The building block, which will be written to a file, so
-            that it can be initialized from it.
-
-        init_functional_groups : :class:`iterable`
-            Passed to the `functional_groups` parameter of
-            :meth:`.BuildingBlock.init_from_file`.
-
-        init_placer_ids : :class:`tuple` or :class:`NoneType`
-            Passed to the `placer_ids` parameter of
-            :meth:`.BuildingBlock.init_from_file`.
-
-        case_data_functional_groups : :class:`tuple`
-            The functional groups the initialized building block should
-            have.
-
-        case_data_core_atom_ids : :class:`tuple` of :class:`int`
-            The ids of core atoms the initialized building block should
-            have.
-
-        case_data_placer_ids : :class:`tuple` of :class:`int`
-            The ids of *placer* atoms the initialized building block
-            should have.
-
-        known_repr : str
-            The representation of the building block.
-
-        """
-
-        self.building_block = building_block
-        self.init_functional_groups = init_functional_groups
-        self.init_placer_ids = init_placer_ids
-        self.case_data_functional_groups = case_data_functional_groups
-        self.case_data_core_atom_ids = case_data_core_atom_ids
-        self.case_data_placer_ids = case_data_placer_ids
-        self.known_repr = known_repr
+    building_block: stk.BuildingBlock
+    init_functional_groups: Sequence[stk.FunctionalGroup]
+    init_placer_ids: Sequence[int] | None
+    case_data_functional_groups: Sequence[stk.FunctionalGroup]
+    case_data_core_atom_ids: Sequence[int]
+    case_data_placer_ids: Sequence[int]
+    known_repr: str
 
 
 @pytest.fixture(
diff --git a/tests/molecular/molecules/building_block/test_get_core_atom_ids.py b/tests/molecular/molecules/building_block/test_get_core_atom_ids.py
index c8b28cb64..73222bd68 100644
--- a/tests/molecular/molecules/building_block/test_get_core_atom_ids.py
+++ b/tests/molecular/molecules/building_block/test_get_core_atom_ids.py
@@ -1,19 +1,16 @@
 import itertools as it
 
+from .case_data import CaseData
 
-def test_get_core_atom_ids(case_data):
+
+def test_get_core_atom_ids(case_data: CaseData) -> None:
     """
     Test :meth:`.BuildingBlock.get_core_atom_ids`.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case. Holds the building block to test and the correct
-        core atom ids.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case. Holds the building block to test and the correct
+            core atom ids.
 
     """
 
diff --git a/tests/molecular/molecules/building_block/test_get_functional_groups.py b/tests/molecular/molecules/building_block/test_get_functional_groups.py
index c6dd4e86e..5664ab69c 100644
--- a/tests/molecular/molecules/building_block/test_get_functional_groups.py
+++ b/tests/molecular/molecules/building_block/test_get_functional_groups.py
@@ -2,20 +2,19 @@
 
 from ..utilities import is_equivalent_functional_group
 
+import stk
+from collections.abc import Sequence
+from .case_data import CaseData
 
-def test_get_functional_groups(case_data):
+
+def test_get_functional_groups(case_data: CaseData) -> None:
     """
     Test :meth:`.BuildingBlock.get_functional_groups`.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case. Holds the building block to test and the correct
-        functional groups.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case. Holds the building block to test and the correct
+            functional groups.
 
     """
 
@@ -25,21 +24,19 @@ def test_get_functional_groups(case_data):
     )
 
 
-def _test_get_functional_groups(building_block, functional_groups):
+def _test_get_functional_groups(
+    building_block: stk.BuildingBlock,
+    functional_groups: Sequence[stk.FunctionalGroup],
+) -> None:
     """
     Test :meth:`.BuildingBlock.get_functional_groups`.
 
-    Parameters
-    ----------
-    building_block : :class:`.BuildingBlock`
-        The building block to test.
-
-    functional_groups : :class:`tuple` of :class:`.FunctionalGroup`
-        The correct functional groups.
+    Parameters:
+        building_block:
+            The building block to test.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        functional_groups:
+            The correct functional groups.
 
     """
 
diff --git a/tests/molecular/molecules/building_block/test_get_num_functional_groups.py b/tests/molecular/molecules/building_block/test_get_num_functional_groups.py
index 22d5db98b..06ec5e0d5 100644
--- a/tests/molecular/molecules/building_block/test_get_num_functional_groups.py
+++ b/tests/molecular/molecules/building_block/test_get_num_functional_groups.py
@@ -1,16 +1,14 @@
-def test_get_num_functional_groups(case_data):
+from .case_data import CaseData
+
+
+def test_get_num_functional_groups(case_data: CaseData) -> None:
     """
     Test :meth:`.BuildingBlock.get_num_functional_groups`.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case. Holds the building block to test and the
-        correct number of functional groups.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case. Holds the building block to test and the correct
+            functional groups.
 
     """
 
diff --git a/tests/molecular/molecules/building_block/test_get_placer_ids.py b/tests/molecular/molecules/building_block/test_get_placer_ids.py
index 7ac1d2b8a..193ab465f 100644
--- a/tests/molecular/molecules/building_block/test_get_placer_ids.py
+++ b/tests/molecular/molecules/building_block/test_get_placer_ids.py
@@ -1,19 +1,17 @@
 import itertools as it
+from .case_data import CaseData
 
+import stk
 
-def test_get_placer_ids(case_data):
+
+def test_get_placer_ids(case_data: CaseData) -> None:
     """
     Test :meth:`.BuildingBlock.get_placer_ids`.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case. Holds the building block to test and the
-        correct placer ids.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case. Holds the building block to test and the
+            correct placer ids.
 
     """
 
@@ -23,21 +21,19 @@ def test_get_placer_ids(case_data):
     )
 
 
-def _test_get_placer_ids(building_block, placer_ids):
+def _test_get_placer_ids(
+    building_block: stk.BuildingBlock,
+    placer_ids: tuple[int, ...],
+) -> None:
     """
     Test :meth:`.BuildingBlock.get_placer_ids`.
 
-    Parameters
-    ----------
-    building_block : :class:`.BuildingBlock`
-        The building block to test.
-
-    placer_ids : :class:`tuple` of :class:`int`
-        The correct placer ids.
+    Parameters:
+        building_block:
+            The building block to test.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        placer_ids:
+            The correct placer ids.
 
     """
 
diff --git a/tests/molecular/molecules/building_block/test_repr.py b/tests/molecular/molecules/building_block/test_repr.py
index ae8735aa5..977230b5c 100644
--- a/tests/molecular/molecules/building_block/test_repr.py
+++ b/tests/molecular/molecules/building_block/test_repr.py
@@ -1,16 +1,15 @@
-def test_repr(case_data):
+from .case_data import CaseData
+
+import stk
+
+
+def test_repr(case_data: CaseData) -> None:
     """
     Test :meth:`.BuildingBlock.__repr__`.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case. Holds the building block to test and the correct
-        functional groups.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case. Holds the building block to test.
 
     """
 
@@ -20,22 +19,18 @@ def test_repr(case_data):
     )
 
 
-def _test_repr(building_block, known_repr):
+def _test_repr(building_block: stk.BuildingBlock, known_repr: str) -> None:
     """
     Test :meth:`.BuildingBlock.get_functional_groups`.
 
-    Parameters
-    ----------
-    building_block : :class:`.BuildingBlock`
-        The building block to test.
-
-    functional_groups : :class:`tuple` of :class:`.FunctionalGroup`
-        The correct functional groups.
+    Parameters:
+        building_block:
+            The building block to test.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        known_repr:
+            The correct representation.
 
     """
+
     print(building_block.__repr__(), known_repr)
     assert building_block.__repr__() == known_repr
diff --git a/tests/molecular/molecules/building_block/test_with_functional_groups.py b/tests/molecular/molecules/building_block/test_with_functional_groups.py
index f52ff9100..819021744 100644
--- a/tests/molecular/molecules/building_block/test_with_functional_groups.py
+++ b/tests/molecular/molecules/building_block/test_with_functional_groups.py
@@ -4,24 +4,26 @@
     is_equivalent_building_block,
     is_equivalent_molecule,
 )
+import stk
+from collections.abc import Sequence, Callable, Iterator
 
 
-def test_with_functional_groups(building_block, get_functional_groups):
+def test_with_functional_groups(
+    building_block: stk.BuildingBlock,
+    get_functional_groups: Callable[
+        [stk.BuildingBlock], Iterator[stk.FunctionalGroup]
+    ],
+) -> None:
     """
     Test :meth:`.BuildingBlock.with_functional_groups`.
 
-    Parameters
-    ----------
-    building_block : :class:`.BuildingBlock`
-        The building block to test.
+    Parameters:
+        building_block:
+            The building block to test.
 
-    get_functional_groups : :class:`callable`
-        Takes a single parameter, `building_block` and returns the
-        `functional_groups` parameter to use for this test.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+        get_functional_groups:
+            Takes a single parameter, `building_block` and returns the
+            `functional_groups` parameter to use for this test.
 
     """
 
@@ -35,21 +37,19 @@ def test_with_functional_groups(building_block, get_functional_groups):
     has_same_structure(building_block, clone)
 
 
-def _test_with_functional_groups(building_block, functional_groups):
+def _test_with_functional_groups(
+    building_block: stk.BuildingBlock,
+    functional_groups: Sequence[stk.FunctionalGroup],
+) -> None:
     """
     Test :meth:`.BuildingBlock.with_functional_groups`.
 
-    Parameters
-    ----------
-    building_block : :class:`.BuildingBlock`
-        The building block to test.
-
-    functional_groups : :class:`tuple` of :class:`.FunctionalGroup`
-        The functional groups the new building block should hold.
+    Parameters:
+        building_block:
+            The building block to test.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        functional_groups:
+            The functional groups the new building block should hold.
 
     """
 
diff --git a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex0.npy b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex0.npy
index ce4d87d46..726a889fe 100644
Binary files a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex0.npy and b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex0.npy differ
diff --git a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex1.npy b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex1.npy
index daa87a20e..59481adc4 100644
Binary files a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex1.npy and b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex1.npy differ
diff --git a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex2.npy b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex2.npy
index daa87a20e..59481adc4 100644
Binary files a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex2.npy and b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex2.npy differ
diff --git a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex3.npy b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex3.npy
index 67b597ccb..91bc24f8e 100644
Binary files a/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex3.npy and b/tests/molecular/molecules/molecule/fixtures/position_matrices/host_guest_complex3.npy differ
diff --git a/tests/molecular/writers/mdl_mol/case_data.py b/tests/molecular/writers/mdl_mol/case_data.py
index b09cd1049..c44ddeae9 100644
--- a/tests/molecular/writers/mdl_mol/case_data.py
+++ b/tests/molecular/writers/mdl_mol/case_data.py
@@ -1,37 +1,10 @@
-class CaseData:
-    """
-    A :class:`.MolWriter` test case.
-
-    Attributes
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.MolWriter`
-        The writer to test.
-
-    string : :class:`str`
-        The expected output string.
-
-    """
+import stk
 
-    def __init__(self, molecule, writer, string):
-        """
-        Initialize a :class:`.CaseData` instance.
+from dataclasses import dataclass
 
-        Parameters
-        ----------
-        molecule : :class:`.Molecule`
-            Molecule to test.
 
-        writer : :class:`.MolWriter`
-            The writer to test.
-
-        string : :class:`str`
-            The expected output string.
-
-        """
-
-        self.molecule = molecule
-        self.writer = writer
-        self.string = string
+@dataclass(slots=True, frozen=True)
+class CaseData:
+    molecule: stk.Molecule
+    writer: stk.MolWriter
+    string: str
diff --git a/tests/molecular/writers/mdl_mol/test_to_string.py b/tests/molecular/writers/mdl_mol/test_to_string.py
index 20cd70ffe..119bee06b 100644
--- a/tests/molecular/writers/mdl_mol/test_to_string.py
+++ b/tests/molecular/writers/mdl_mol/test_to_string.py
@@ -1,15 +1,15 @@
-def test_to_string(case_data):
+import stk
+
+from .case_data import CaseData
+
+
+def test_to_string(case_data: CaseData) -> None:
     """
     Test writing of molecule to a string.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case.
 
     """
 
@@ -20,24 +20,23 @@ def test_to_string(case_data):
     )
 
 
-def _test_to_string(molecule, writer, string):
+def _test_to_string(
+    molecule: stk.Molecule,
+    writer: stk.MolWriter,
+    string: str,
+) -> None:
     """
     Test that the written string matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.MolWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        string:
+            The expected output string.
 
     """
 
diff --git a/tests/molecular/writers/mdl_mol/test_write.py b/tests/molecular/writers/mdl_mol/test_write.py
index 751059e64..be73a0d21 100644
--- a/tests/molecular/writers/mdl_mol/test_write.py
+++ b/tests/molecular/writers/mdl_mol/test_write.py
@@ -1,18 +1,19 @@
-def test_write(case_data, tmp_path):
+import stk
+
+from .case_data import CaseData
+import pathlib
+
+
+def test_write(case_data: CaseData, tmp_path: pathlib.Path) -> None:
     """
     Test writing of molecule to a file.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
+    Parameters:
+        case_data:
+            A test case.
 
-    tmp_path : :class:`pathlib2.Path`
-        Path to temporary directory.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+        tmp_path:
+            Path to temporary directory.
 
     """
 
@@ -24,27 +25,27 @@ def test_write(case_data, tmp_path):
     )
 
 
-def _test_write(molecule, writer, string, file_path):
+def _test_write(
+    molecule: stk.Molecule,
+    writer: stk.MolWriter,
+    string: str,
+    file_path: pathlib.Path,
+) -> None:
     """
     Test that the written file content matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.MolWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    file_path : :class:`str`
-        Path to temporary file.
+        string:
+            The expected output string.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        file_path:
+            Path to temporary file.
 
     """
 
diff --git a/tests/molecular/writers/pdb/case_data.py b/tests/molecular/writers/pdb/case_data.py
index 8392c829c..f62af625e 100644
--- a/tests/molecular/writers/pdb/case_data.py
+++ b/tests/molecular/writers/pdb/case_data.py
@@ -1,45 +1,11 @@
-class CaseData:
-    """
-    A :class:`.PdbWriter` test case.
-
-    Attributes
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.PdbWriter`
-        The writer to test.
-
-    string : :class:`str`
-        The expected output string.
-
-    periodic_info : :class:`.PeriodicInfo`
-        Information about periodic cell. Required for testing writing
-        of constructed molecules with periodic unit cells.
-
-    """
+import stk
 
-    def __init__(self, molecule, writer, string, periodic_info):
-        """
-        Initialize a :class:`.CaseData` instance.
+from dataclasses import dataclass
 
-        Parameters
-        ----------
-        molecule : :class:`.Molecule`
-            Molecule to test.
 
-        writer : :class:`.PdbWriter`
-            The writer to test.
-
-        string : :class:`str`
-            The expected output string.
-
-        periodic_info : :class:`.PeriodicInfo`
-            Information about periodic cell.
-
-        """
-
-        self.molecule = molecule
-        self.writer = writer
-        self.string = string
-        self.periodic_info = periodic_info
+@dataclass(slots=True, frozen=True)
+class CaseData:
+    molecule: stk.Molecule
+    writer: stk.PdbWriter
+    string: str
+    periodic_info: stk.PeriodicInfo | None
diff --git a/tests/molecular/writers/pdb/conftest.py b/tests/molecular/writers/pdb/conftest.py
index 6aeae6a62..bfea4490d 100644
--- a/tests/molecular/writers/pdb/conftest.py
+++ b/tests/molecular/writers/pdb/conftest.py
@@ -109,7 +109,7 @@ def _get_cof_case() -> CaseData:
             "  30               \nCONECT    3   35               "
             "\nCONECT   14   36               \nEND\n"
         ),
-        periodic_info=construction_result.get_periodic_info(),
+        periodic_info=construction_result.get_periodic_info(),  # type: ignore[attr-defined]
     )
 
 
diff --git a/tests/molecular/writers/pdb/test_to_string.py b/tests/molecular/writers/pdb/test_to_string.py
index 74a16aff1..1b36c8e98 100644
--- a/tests/molecular/writers/pdb/test_to_string.py
+++ b/tests/molecular/writers/pdb/test_to_string.py
@@ -1,15 +1,15 @@
-def test_to_string(case_data):
+import stk
+
+from .case_data import CaseData
+
+
+def test_to_string(case_data: CaseData) -> None:
     """
     Test writing of molecule to a string.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case.
 
     """
 
@@ -21,27 +21,27 @@ def test_to_string(case_data):
     )
 
 
-def _test_to_string(molecule, writer, string, periodic_info=None):
+def _test_to_string(
+    molecule: stk.Molecule,
+    writer: stk.PdbWriter,
+    string: str,
+    periodic_info: stk.PeriodicInfo | None = None,
+) -> None:
     """
     Test that the written string matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.PdbWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    periodic_info : :class:`.PeriodicInfo`
-        Periodic information.
+        string:
+            The expected output string.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        periodic_info:
+            Periodic information.
 
     """
 
diff --git a/tests/molecular/writers/pdb/test_write.py b/tests/molecular/writers/pdb/test_write.py
index c9fb786a4..2d5a5edd0 100644
--- a/tests/molecular/writers/pdb/test_write.py
+++ b/tests/molecular/writers/pdb/test_write.py
@@ -1,18 +1,19 @@
-def test_write(case_data, tmp_path):
+import stk
+
+from .case_data import CaseData
+import pathlib
+
+
+def test_write(case_data: CaseData, tmp_path: pathlib.Path) -> None:
     """
     Test writing of molecule to a file.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
+    Parameters:
+        case_data:
+            A test case.
 
-    tmp_path : :class:`pathlib2.Path`
-        Path to temporary directory.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+        tmp_path:
+            Path to temporary directory.
 
     """
 
@@ -26,35 +27,30 @@ def test_write(case_data, tmp_path):
 
 
 def _test_write(
-    molecule,
-    writer,
-    string,
-    file_path,
-    periodic_info=None,
+    molecule: stk.Molecule,
+    writer: stk.PdbWriter,
+    string: str,
+    file_path: pathlib.Path,
+    periodic_info: stk.PeriodicInfo | None = None,
 ):
     """
     Test that the written file content matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.PdbWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    periodic_info : :class:`.PeriodicInfo`
-        Periodic information.
+        string:
+            The expected output string.
 
-    file_path : :class:`str`
-        Path to temporary file.
+        file_path:
+            Path to temporary file.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        periodic_info:
+            Periodic information.
 
     """
 
diff --git a/tests/molecular/writers/turbomole/case_data.py b/tests/molecular/writers/turbomole/case_data.py
index 475580943..42edaa19c 100644
--- a/tests/molecular/writers/turbomole/case_data.py
+++ b/tests/molecular/writers/turbomole/case_data.py
@@ -1,45 +1,11 @@
-class CaseData:
-    """
-    A :class:`.TurbomoleWriter` test case.
-
-    Attributes
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.TurbomoleWriter`
-        The writer to test.
-
-    string : :class:`str`
-        The expected output string.
-
-    periodic_info : :class:`.PeriodicInfo`
-        Information about periodic cell. Required for testing writing
-        of constructed molecules with periodic unit cells.
-
-    """
+import stk
 
-    def __init__(self, molecule, writer, string, periodic_info):
-        """
-        Initialize a :class:`.CaseData` instance.
+from dataclasses import dataclass
 
-        Parameters
-        ----------
-        molecule : :class:`.Molecule`
-            Molecule to test.
 
-        writer : :class:`.TurbomoleWriter`
-            The writer to test.
-
-        string : :class:`str`
-            The expected output string.
-
-        periodic_info : :class:`.PeriodicInfo`
-            Information about periodic cell.
-
-        """
-
-        self.molecule = molecule
-        self.writer = writer
-        self.string = string
-        self.periodic_info = periodic_info
+@dataclass(slots=True, frozen=True)
+class CaseData:
+    molecule: stk.Molecule
+    writer: stk.TurbomoleWriter
+    string: str
+    periodic_info: stk.PeriodicInfo | None
diff --git a/tests/molecular/writers/turbomole/conftest.py b/tests/molecular/writers/turbomole/conftest.py
index f041585e8..eb7ec3835 100644
--- a/tests/molecular/writers/turbomole/conftest.py
+++ b/tests/molecular/writers/turbomole/conftest.py
@@ -43,7 +43,7 @@ def _get_cof_case() -> CaseData:
             "1.6749 H\n 7.9667 16.1026 53.582 H\n 7.7801 15.8075 5"
             "1.7756 H\n$end\n"
         ),
-        periodic_info=construction_result.get_periodic_info(),
+        periodic_info=construction_result.get_periodic_info(),  # type: ignore[attr-defined]
     )
 
 
diff --git a/tests/molecular/writers/turbomole/test_to_string.py b/tests/molecular/writers/turbomole/test_to_string.py
index 498bc3aa8..c0d81f1fc 100644
--- a/tests/molecular/writers/turbomole/test_to_string.py
+++ b/tests/molecular/writers/turbomole/test_to_string.py
@@ -1,15 +1,15 @@
-def test_to_string(case_data):
+import stk
+
+from .case_data import CaseData
+
+
+def test_to_string(case_data: CaseData) -> None:
     """
     Test writing of molecule to a string.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case.
 
     """
 
@@ -21,27 +21,27 @@ def test_to_string(case_data):
     )
 
 
-def _test_to_string(molecule, writer, string, periodic_info=None):
+def _test_to_string(
+    molecule: stk.Molecule,
+    writer: stk.TurbomoleWriter,
+    string: str,
+    periodic_info: stk.PeriodicInfo | None = None,
+) -> None:
     """
     Test that the written string matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.TurbomoleWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    periodic_info : :class:`.PeriodicInfo`
-        Periodic information.
+        string:
+            The expected output string.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        periodic_info:
+            Periodic information.
 
     """
 
diff --git a/tests/molecular/writers/turbomole/test_write.py b/tests/molecular/writers/turbomole/test_write.py
index c64e11d83..7f63372a2 100644
--- a/tests/molecular/writers/turbomole/test_write.py
+++ b/tests/molecular/writers/turbomole/test_write.py
@@ -1,21 +1,21 @@
-def test_write(case_data, tmp_path):
+import stk
+
+from .case_data import CaseData
+import pathlib
+
+
+def test_write(case_data: CaseData, tmp_path: pathlib.Path) -> None:
     """
     Test writing of molecule to a file.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
+    Parameters:
+        case_data:
+            A test case.
 
-    tmp_path : :class:`pathlib2.Path`
-        Path to temporary directory.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+        tmp_path:
+            Path to temporary directory.
 
     """
-
     _test_write(
         molecule=case_data.molecule,
         writer=case_data.writer,
@@ -26,35 +26,30 @@ def test_write(case_data, tmp_path):
 
 
 def _test_write(
-    molecule,
-    writer,
-    string,
-    file_path,
-    periodic_info=None,
+    molecule: stk.Molecule,
+    writer: stk.TurbomoleWriter,
+    string: str,
+    file_path: pathlib.Path,
+    periodic_info: stk.PeriodicInfo | None = None,
 ):
     """
     Test that the written file content matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.TurbomoleWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    periodic_info : :class:`.PeriodicInfo`
-        Periodic information.
+        string:
+            The expected output string.
 
-    file_path : :class:`str`
-        Path to temporary file.
+        file_path:
+            Path to temporary file.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        periodic_info:
+            Periodic information.
 
     """
 
diff --git a/tests/molecular/writers/xyz/case_data.py b/tests/molecular/writers/xyz/case_data.py
index 13a6c1060..962c5fc4e 100644
--- a/tests/molecular/writers/xyz/case_data.py
+++ b/tests/molecular/writers/xyz/case_data.py
@@ -1,37 +1,10 @@
-class CaseData:
-    """
-    A :class:`.XyzWriter` test case.
-
-    Attributes
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.XyzWriter`
-        The writer to test.
-
-    string : :class:`str`
-        The expected output string.
-
-    """
+import stk
 
-    def __init__(self, molecule, writer, string):
-        """
-        Initialize a :class:`.CaseData` instance.
+from dataclasses import dataclass
 
-        Parameters
-        ----------
-        molecule : :class:`.Molecule`
-            Molecule to test.
 
-        writer : :class:`.XyzWriter`
-            The writer to test.
-
-        string : :class:`str`
-            The expected output string.
-
-        """
-
-        self.molecule = molecule
-        self.writer = writer
-        self.string = string
+@dataclass(slots=True, frozen=True)
+class CaseData:
+    molecule: stk.Molecule
+    writer: stk.XyzWriter
+    string: str
diff --git a/tests/molecular/writers/xyz/test_to_string.py b/tests/molecular/writers/xyz/test_to_string.py
index c13ca7952..c56ae2f35 100644
--- a/tests/molecular/writers/xyz/test_to_string.py
+++ b/tests/molecular/writers/xyz/test_to_string.py
@@ -1,15 +1,15 @@
-def test_to_string(case_data):
+import stk
+
+from .case_data import CaseData
+
+
+def test_to_string(case_data: CaseData) -> None:
     """
     Test writing of molecule to a string.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+    Parameters:
+        case_data:
+            A test case.
 
     """
 
@@ -20,24 +20,23 @@ def test_to_string(case_data):
     )
 
 
-def _test_to_string(molecule, writer, string):
+def _test_to_string(
+    molecule: stk.Molecule,
+    writer: stk.XyzWriter,
+    string: str,
+) -> None:
     """
     Test that the written string matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.XyzWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        string:
+            The expected output string.
 
     """
 
diff --git a/tests/molecular/writers/xyz/test_write.py b/tests/molecular/writers/xyz/test_write.py
index aa8bccb75..d02452ba6 100644
--- a/tests/molecular/writers/xyz/test_write.py
+++ b/tests/molecular/writers/xyz/test_write.py
@@ -1,18 +1,19 @@
-def test_write(case_data, tmp_path):
+import stk
+
+from .case_data import CaseData
+import pathlib
+
+
+def test_write(case_data: CaseData, tmp_path: pathlib.Path) -> None:
     """
     Test writing of molecule to a file.
 
-    Parameters
-    ----------
-    case_data : :class:`.CaseData`
-        A test case.
+    Parameters:
+        case_data:
+            A test case.
 
-    tmp_path : :class:`pathlib2.Path`
-        Path to temporary directory.
-
-    Returns
-    -------
-    None : :class:`NoneType`
+        tmp_path:
+            Path to temporary directory.
 
     """
 
@@ -24,27 +25,27 @@ def test_write(case_data, tmp_path):
     )
 
 
-def _test_write(molecule, writer, string, file_path):
+def _test_write(
+    molecule: stk.Molecule,
+    writer: stk.XyzWriter,
+    string: str,
+    file_path: pathlib.Path,
+) -> None:
     """
     Test that the written file content matches expected string.
 
-    Parameters
-    ----------
-    molecule : :class:`.Molecule`
-        Molecule to test.
-
-    writer : :class:`.XyzWriter`
-        The writer to test.
+    Parameters:
+        molecule:
+            Molecule to test.
 
-    string : :class:`str`
-        The expected output string.
+        writer:
+            The writer to test.
 
-    file_path : :class:`str`
-        Path to temporary file.
+        string:
+            The expected output string.
 
-    Returns
-    -------
-    None : :class:`NoneType`
+        file_path:
+            Path to temporary file.
 
     """