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Fix unittest.mock.patch and unittest.mock.patch.object when new_callable is not None #14358

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Fix unittest.mock.patch and unittest.mock.patch.object when new_callable is not None #14358

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f5ca09a
Fix patch and patch.object when new_callable is not None
leonarduschen Jul 1, 2025
fa964f3
Add new test cases
leonarduschen Jul 2, 2025
cb35c54
Fix patch and patch.object as function decorator
leonarduschen Jul 2, 2025
19deb1c
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jul 2, 2025
ade3152
Use typing.Union
leonarduschen Jul 2, 2025
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59 changes: 57 additions & 2 deletions stdlib/@tests/test_cases/check_unittest.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,9 +5,9 @@
from datetime import datetime, timedelta
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Test result with old implementation

check_unittest.py:190: error: Expression is of type "MagicMock | AsyncMock", not "int"  [assert-type]
check_unittest.py:213: error: Missing positional argument "mock" in call to "obj_f_default_new"  [call-arg]
check_unittest.py:214: error: Missing positional argument "mock" in call to "obj_f_default_new"  [call-arg]
check_unittest.py:214: error: Argument 1 to "obj_f_default_new" has incompatible type "str"; expected "int"  [arg-type]
check_unittest.py:217: error: Missing positional argument "new_callable_ret" in call to "obj_f_explicit_new_callable"  [call-arg]
check_unittest.py:218: error: Missing positional argument "new_callable_ret" in call to "obj_f_explicit_new_callable"  [call-arg]
check_unittest.py:218: error: Argument 1 to "obj_f_explicit_new_callable" has incompatible type "str"; expected "int"  [arg-type]
check_unittest.py:228: error: Expression is of type "MagicMock | AsyncMock", not "int"  [assert-type]

This agrees with the upated PR description:

This PR fixes multiple issues with unittest.mock.patch and unittest.mock.patch.object

  • Both should only accept Callable | None for new_callable, currently Any | None

  • When used as context managers, both should return T for new_callable: Callable[..., T], currently they both return Mock | AsyncMock

  • When used as decorators to functions:

    • When neither new nor new_callable is given, the function signature should be updated (the mock is passed as last parameter), patch already has the correct behavior but patch.object does not
    • When new_callable is given, same as above, should update function signature. patch already has the correct behavior (by chance, explicit new_callable is not actually handled), but patch.object does not

from decimal import Decimal
from fractions import Fraction
from typing import TypedDict
from typing import TypedDict, Union
from typing_extensions import assert_type
from unittest.mock import MagicMock, Mock, patch
from unittest.mock import AsyncMock, MagicMock, Mock, patch

case = unittest.TestCase()

Expand Down Expand Up @@ -154,10 +154,17 @@ def f_explicit_new(i: int) -> str:
return "asdf"


@patch("sys.exit", new_callable=lambda: 42)
def f_explicit_new_callable(i: int, new_callable_ret: int) -> str:
return "asdf"


assert_type(f_default_new(1), str)
f_default_new("a") # Not an error due to ParamSpec limitations
assert_type(f_explicit_new(1), str)
f_explicit_new("a") # type: ignore[arg-type]
assert_type(f_explicit_new_callable(1), str)
f_explicit_new_callable("a") # Same as default new


@patch("sys.exit", new=Mock())
Expand All @@ -171,3 +178,51 @@ def method() -> int:

assert_type(TestXYZ.attr, int)
assert_type(TestXYZ.method(), int)


with patch("sys.exit") as default_new_enter:
assert_type(default_new_enter, Union[MagicMock, AsyncMock])

with patch("sys.exit", new=42) as explicit_new_enter:
assert_type(explicit_new_enter, int)

with patch("sys.exit", new_callable=lambda: 42) as explicit_new_callable_enter:
assert_type(explicit_new_callable_enter, int)


###
# Tests for mock.patch.object
###


@patch.object(Decimal, "exp")
def obj_f_default_new(i: int, mock: MagicMock) -> str:
return "asdf"


@patch.object(Decimal, "exp", new=42)
def obj_f_explicit_new(i: int) -> str:
return "asdf"


@patch.object(Decimal, "exp", new_callable=lambda: 42)
def obj_f_explicit_new_callable(i: int, new_callable_ret: int) -> str:
return "asdf"


assert_type(obj_f_default_new(1), str)
obj_f_default_new("a") # Not an error due to ParamSpec limitations
assert_type(obj_f_explicit_new(1), str)
obj_f_explicit_new("a") # type: ignore[arg-type]
assert_type(obj_f_explicit_new_callable(1), str)
obj_f_explicit_new_callable("a") # Same as default new


with patch.object(Decimal, "exp") as obj_default_new_enter:
assert_type(obj_default_new_enter, Union[MagicMock, AsyncMock])

with patch.object(Decimal, "exp", new=42) as obj_explicit_new_enter:
assert_type(obj_explicit_new_enter, int)

with patch.object(Decimal, "exp", new_callable=lambda: 42) as obj_explicit_new_callable_enter:
assert_type(obj_explicit_new_callable_enter, int)
39 changes: 32 additions & 7 deletions stdlib/unittest/mock.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -262,7 +262,7 @@ class _patch(Generic[_T]):
# This class does not exist at runtime, it's a hack to make this work:
# @patch("foo")
# def bar(..., mock: MagicMock) -> None: ...
class _patch_default_new(_patch[MagicMock | AsyncMock]):
class _patch_pass_arg(_patch[_T]):
@overload
def __call__(self, func: _TT) -> _TT: ...
# Can't use the following as ParamSpec is only allowed as last parameter:
Expand Down Expand Up @@ -303,7 +303,7 @@ class _patcher:
create: bool = ...,
spec_set: Any | None = ...,
autospec: Any | None = ...,
new_callable: Any | None = ...,
new_callable: Callable[..., Any] | None = ...,
**kwargs: Any,
) -> _patch[_T]: ...
@overload
Expand All @@ -315,9 +315,21 @@ class _patcher:
create: bool = ...,
spec_set: Any | None = ...,
autospec: Any | None = ...,
new_callable: Any | None = ...,
new_callable: Callable[..., _T],
**kwargs: Any,
) -> _patch_default_new: ...
) -> _patch_pass_arg[_T]: ...
@overload
def __call__(
self,
target: str,
*,
spec: Any | None = ...,
create: bool = ...,
spec_set: Any | None = ...,
autospec: Any | None = ...,
new_callable: None = ...,
**kwargs: Any,
) -> _patch_pass_arg[MagicMock | AsyncMock]: ...
@overload
@staticmethod
def object(
Expand All @@ -328,7 +340,7 @@ class _patcher:
create: bool = ...,
spec_set: Any | None = ...,
autospec: Any | None = ...,
new_callable: Any | None = ...,
new_callable: Callable[..., Any] | None = ...,
**kwargs: Any,
) -> _patch[_T]: ...
@overload
Expand All @@ -341,9 +353,22 @@ class _patcher:
create: bool = ...,
spec_set: Any | None = ...,
autospec: Any | None = ...,
new_callable: Any | None = ...,
new_callable: Callable[..., _T],
**kwargs: Any,
) -> _patch_pass_arg[_T]: ...
@overload
@staticmethod
def object(
target: Any,
attribute: str,
*,
spec: Any | None = ...,
create: bool = ...,
spec_set: Any | None = ...,
autospec: Any | None = ...,
new_callable: None = ...,
**kwargs: Any,
) -> _patch[MagicMock | AsyncMock]: ...
) -> _patch_pass_arg[MagicMock | AsyncMock]: ...
@staticmethod
def multiple(
target: Any,
Expand Down