diff --git a/tests/test_types.py b/tests/test_types.py
new file mode 100644
index 0000000..614ecf4
--- /dev/null
+++ b/tests/test_types.py
@@ -0,0 +1,83 @@
+from typing import Any
+
+import tomlkit
+
+from tomlkit._types import wrap_method
+from tomlkit.items import Array
+from tomlkit.items import Table
+
+
+def test_custom_list_add_returns_plain_list_with_combined_items() -> None:
+    arr = tomlkit.array()
+    arr.extend([1, 2, 3])
+
+    result = arr + [4, 5]  # noqa: RUF005 (exercising __add__ itself)
+
+    assert result == [1, 2, 3, 4, 5]
+    assert not isinstance(result, Array)
+
+
+def test_custom_list_iadd_mutates_in_place_and_keeps_wrapper_type() -> None:
+    arr = tomlkit.array()
+    arr.extend([1, 2])
+    original_id = id(arr)
+
+    arr += [9]
+
+    assert arr == [1, 2, 9]
+    assert isinstance(arr, Array)
+    assert id(arr) == original_id
+
+
+def test_custom_dict_or_returns_new_table_with_merged_items() -> None:
+    table = tomlkit.table()
+    table["a"] = 1
+    table["b"] = 2
+
+    result = table | {"c": 3}
+
+    assert dict(result) == {"a": 1, "b": 2, "c": 3}
+    assert isinstance(result, Table)
+    assert result is not table
+
+
+def test_custom_dict_ior_mutates_in_place() -> None:
+    table = tomlkit.table()
+    table["x"] = 1
+    original_id = id(table)
+
+    table |= {"y": 2}
+
+    assert dict(table) == {"x": 1, "y": 2}
+    assert id(table) == original_id
+
+
+class _Wrapped:
+    def __init__(self, value: int) -> None:
+        self.value = value
+
+    def _new(self, value: int) -> "_Wrapped":
+        return _Wrapped(value)
+
+
+def test_wrap_method_wraps_result_via_new() -> None:
+    def raw_add(self: _Wrapped, other: int) -> int:
+        return self.value + other
+
+    wrapped_add = wrap_method(raw_add)
+    wrapped = _Wrapped(5)
+
+    result = wrapped_add(wrapped, 3)
+
+    assert isinstance(result, _Wrapped)
+    assert result.value == 8
+
+
+def test_wrap_method_passes_through_not_implemented() -> None:
+    def raw_not_implemented(self: _Wrapped, other: int) -> Any:
+        return NotImplemented
+
+    wrapped_method = wrap_method(raw_not_implemented)
+    wrapped = _Wrapped(5)
+
+    assert wrapped_method(wrapped, 3) is NotImplemented