diff --git a/tests/helpers.py b/tests/helpers.py
index 161b793..d21d6c6 100644
--- a/tests/helpers.py
+++ b/tests/helpers.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 
 import asyncio
 import unittest.mock
-from typing import Any, ClassVar, Generic, TYPE_CHECKING, TypeVar
+from typing import Any, Generic, TYPE_CHECKING, TypeVar
 
 from typing_extensions import ParamSpec
 
@@ -70,7 +70,7 @@ class UnpropagatingMockMixin(Generic[T_Mock]):
     _mock_sealed: bool
     _extract_mock_name: Callable[[], str]
 
-    def _get_child_mock(self, **kwargs: object) -> T_Mock:
+    def _get_child_mock(self, **kwargs) -> T_Mock:
         """Make :attr:`.child_mock_type`` instances instead of instances of the same class.
 
         By default, this method creates a new mock instance of the same original class, and passes
@@ -84,12 +84,12 @@ class UnpropagatingMockMixin(Generic[T_Mock]):
             obj_name = f"{mock_name}.{kwargs['name']}" if "name" in kwargs else f"{mock_name}()"
             raise AttributeError(f"Can't access {obj_name}, mock is sealed.")
 
-        # Propagate any other children as the `child_mock_type` instances
+        # Propagate any other children as simple `unittest.mock.Mock` instances
         # rather than `self.__class__` instances
         return self.child_mock_type(**kwargs)
 
 
-class CustomMockMixin(UnpropagatingMockMixin[T_Mock], Generic[T_Mock]):
+class CustomMockMixin(UnpropagatingMockMixin):
     """Provides common functionality for our custom mock types.
 
     * Stops propagation of same ``spec_set`` restricted mock in child mocks
@@ -97,16 +97,9 @@ class CustomMockMixin(UnpropagatingMockMixin[T_Mock], Generic[T_Mock]):
     * Allows using the ``spec_set`` attribute as class attribute
     """
 
-    spec_set: ClassVar[object] = None
+    spec_set = None
 
-    def __init__(self, **kwargs: object):
-        # If `spec_set` is explicitly passed, have it take precedence over the class attribute.
-        #
-        # Although this is an edge case, and there usually shouldn't be a need for this.
-        # This is mostly for the sake of completeness, and to allow for more flexibility.
+    def __init__(self, **kwargs):
         if "spec_set" in kwargs:
-            spec_set = kwargs.pop("spec_set")
-        else:
-            spec_set = self.spec_set
-
-        super().__init__(spec_set=spec_set, **kwargs)  # pyright: ignore[reportCallIssue]  # Mixin class, this __init__ is valid
+            self.spec_set = kwargs.pop("spec_set")
+        super().__init__(spec_set=self.spec_set, **kwargs)  # type: ignore # Mixin class, this __init__ is valid
diff --git a/tests/test_helpers.py b/tests/test_helpers.py
deleted file mode 100644
index 194cf22..0000000
--- a/tests/test_helpers.py
+++ /dev/null
@@ -1,58 +0,0 @@
-from unittest.mock import MagicMock, Mock
-
-from tests.helpers import CustomMockMixin, UnpropagatingMockMixin, synchronize
-
-
-def test_synchronize():
-    """Test the :func:`synchronize` helper function."""
-
-    async def test_func(x: int) -> int:
-        if x == 5:
-            return 10
-        return 0
-
-    assert synchronize(test_func)(5) == 10
-    assert synchronize(test_func)(6) == 0
-
-
-def test_unpropagating_mock_mixin():
-    """Test the :class:`UnpropagatingMockMixin` helper class.
-
-    Mocks that inherit from this mixin should not propagate themselves when new attributes are accessed.
-    Instead, a general mock (of the generic type) should be returned. By default, this is a :class:`MagicMock`.
-    """
-
-    class MyUnpropagatingMock(UnpropagatingMockMixin[MagicMock], Mock): ...
-
-    x = MyUnpropagatingMock(spec_set=str)
-
-    # Test that the `spec_set` works as expected
-    assert hasattr(x, "removesuffix")
-    assert not hasattr(x, "notastringmethod")
-
-    unpropagated_mock = x.removesuffix()
-
-    # Test that the resulting mock behaves without spec_set
-    assert hasattr(unpropagated_mock, "removesuffix")
-    assert hasattr(unpropagated_mock, "notastringmethod")
-
-
-def test_custom_mock_mixin():
-    """Test the :class:`CustomMockMixin` helper class.
-
-    This class is very similar to :class:`UnpropagatingMockMixin`, with the only difference being that it
-    supports setting ``spec_set`` as a class variable.
-    """
-
-    class MyCustomMock(CustomMockMixin[MagicMock], Mock):  # pyright: ignore[reportUnsafeMultipleInheritance]
-        spec_set = str
-
-    # Test that the mock really has the `spec_set` of `str` by default
-    x = MyCustomMock()
-    assert hasattr(x, "removesuffix")
-    assert not hasattr(x, "notastringmethod")
-
-    # Explicitly setting `spec_set` on __init__ should take precedence
-    y = MyCustomMock(spec_set=int)
-    assert not hasattr(y, "removesuffix")
-    assert hasattr(y, "to_bytes")