diff --git a/tests/test_helpers.py b/tests/test_helpers.py
new file mode 100644
index 0000000..194cf22
--- /dev/null
+++ b/tests/test_helpers.py
@@ -0,0 +1,58 @@
+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")