fix: consume self argument of builtin methods (#326)

Author: mcous

decoy/next/_internal/inspect.py

@@ -105,8 +105,8 @@ def get_child_spec(spec: object, child_name: str) -> object:
                 _get_type_hints(unwrapped_child_source.fget).get("return")
             )
 
-        if inspect.isfunction(unwrapped_child_source):
-            # consume `self` argument
+        # consume `self` and `cls` arguments
+        if inspect.isroutine(unwrapped_child_source):
             return functools.partial(unwrapped_child_source, None)
 
         return _unwrap_type_alias(unwrapped_child_source)

decoy/spy_core.py

@@ -1,17 +1,17 @@
 """Core spy logic."""
 
-import inspect
 import functools
+import inspect
 import warnings
 from typing import (
     Any,
     Dict,
     NamedTuple,
     Optional,
+    Sequence,
     Tuple,
     Type,
     Union,
-    Sequence,
     get_type_hints,
 )
 
@@ -142,7 +142,7 @@ def create_child_core(self, name: str, is_async: bool) -> "SpyCore":
 
                 child_source = inspect.unwrap(child_source)
 
-                if inspect.isfunction(child_source):
+                if inspect.isroutine(child_source):
                     # consume the `self` argument of the method to ensure proper
                     # signature reporting by wrapping it in a partial
                     child_source = functools.partial(child_source, None)

tests/legacy/test_mock.py

@@ -1,5 +1,6 @@
 """Smoke and acceptance tests for main Decoy interface."""
 
+import asyncio
 import inspect
 import sys
 from typing import Any
@@ -327,3 +328,13 @@ async def test_async_context_manager(decoy: Decoy) -> None:
 
     async with subject as result:
         assert result is None
+
+
+@pytest.mark.skipif(sys.version_info < (3, 9), reason="msg param added in 3.9")
+def test_builtin(decoy: Decoy) -> None:
+    """It can mock builtin classes."""
+    subject = decoy.mock(cls=asyncio.Task)
+    subject.cancel(msg="hello")
+
+    with pytest.warns(IncorrectCallWarning):
+        subject.cancel(message="oops")  # type: ignore[call-arg]

tests/test_mock.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import asyncio
 import inspect
 import sys
 from typing import Any
@@ -364,3 +365,12 @@ async def test_async_context_manager(decoy: Decoy) -> None:
 
     async with subject as result:
         assert result is None
+
+
+def test_builtin(decoy: Decoy) -> None:
+    """It can mock builtin classes."""
+    subject = decoy.mock(cls=asyncio.Task)
+    subject.cancel(msg="hello")
+
+    with pytest.raises(errors.SignatureMismatchError):
+        subject.cancel(message="oops")  # type: ignore[call-arg]