cleanup patches after test in pytest plugin (#1148) (#1164)

* cleanup patches after test in pytest plugin (#1148)

* pin dependency in docs causing problems with breaking change

* simplify Generator annotations; use mapping proxy to ensure immutable module constant

CHANGELOG.md

@@ -10,6 +10,7 @@ See [0Ver](https://0ver.org/).
 ### Bugfixes
 
 - Fixes `__slots__` not being set properly in containers and their base classes
+- Fixes patching of containers in pytest plugin not undone after each test
 
 ## 0.17.0
 

docs/requirements.txt

@@ -20,3 +20,7 @@ hypothesis==6.30.1
 # TODO: Remove this lock when we found and fix the route case.
 # See: https://github.com/typlog/sphinx-typlog-theme/issues/22
 jinja2==3.0.3
+
+# TODO: Remove this lock when this dependency issue is resolved.
+# See: https://github.com/miyakogi/m2r/issues/66
+mistune<2.0.0

returns/contrib/pytest/plugin.py

@@ -1,24 +1,17 @@
 import inspect
 import sys
-from contextlib import contextmanager
+from contextlib import ExitStack, contextmanager
 from functools import partial, wraps
-from types import FrameType
+from types import FrameType, MappingProxyType
 from typing import TYPE_CHECKING, Any, Callable, Dict, Iterator, TypeVar, Union
+from unittest import mock
 
 import pytest
 from typing_extensions import Final, final
 
 if TYPE_CHECKING:
     from returns.interfaces.specific.result import ResultLikeN
 
-_ERROR_HANDLERS: Final = (
-    'lash',
-)
-_ERRORS_COPIERS: Final = (
-    'map',
-    'alt',
-)
-
 # We keep track of errors handled by keeping a mapping of <object id>: object.
 # If an error is handled, it is in the mapping.
 # If it isn't in the mapping, the error is not handled.
@@ -28,7 +21,7 @@
 # Also, the object itself cannot be (in) the key because
 # (1) we cannot always assume hashability and
 # (2) we need to track the object identity, not its value
-_ERRORS_HANDLED: Final[Dict[int, Any]] = {}  # noqa: WPS407
+_ErrorsHandled = Dict[int, Any]
 
 _FunctionType = TypeVar('_FunctionType', bound=Callable)
 _ReturnsResultType = TypeVar(
@@ -41,7 +34,11 @@
 class ReturnsAsserts(object):
     """Class with helpers assertions to check containers."""
 
-    __slots__ = ()
+    __slots__ = ('_errors_handled', )
+
+    def __init__(self, errors_handled: _ErrorsHandled) -> None:
+        """Constructor for this type."""
+        self._errors_handled = errors_handled
 
     @staticmethod  # noqa: WPS602
     def assert_equal(  # noqa: WPS602
@@ -55,10 +52,9 @@ def assert_equal(  # noqa: WPS602
         from returns.primitives.asserts import assert_equal
         assert_equal(first, second, deps=deps, backend=backend)
 
-    @staticmethod  # noqa: WPS602
-    def is_error_handled(container) -> bool:  # noqa: WPS602
+    def is_error_handled(self, container) -> bool:
         """Ensures that container has its error handled in the end."""
-        return id(container) in _ERRORS_HANDLED
+        return id(container) in self._errors_handled
 
     @staticmethod  # noqa: WPS602
     @contextmanager
@@ -86,59 +82,6 @@ def assert_trace(  # noqa: WPS602
             sys.settrace(old_tracer)
 
 
-@pytest.fixture(scope='session')
-def returns(_patch_containers) -> ReturnsAsserts:
-    """Returns our own class with helpers assertions to check containers."""
-    return ReturnsAsserts()
-
-
-@pytest.fixture(autouse=True)
-def _clear_errors_handled():
-    """Ensures the 'errors handled' registry doesn't leak memory."""
-    yield
-    _ERRORS_HANDLED.clear()
-
-
-def pytest_configure(config) -> None:
-    """
-    Hook to be executed on import.
-
-    We use it define custom markers.
-    """
-    config.addinivalue_line(
-        'markers',
-        (
-            'returns_lawful: all tests under `check_all_laws` ' +
-            'is marked this way, ' +
-            'use `-m "not returns_lawful"` to skip them.'
-        ),
-    )
-
-
-@pytest.fixture(scope='session')
-def _patch_containers() -> None:
-    """
-    Fixture to add test specifics into our containers.
-
-    Currently we inject:
-
-    - Error handling state, this is required to test that ``Result``-based
-      containers do handle errors
-
-    Even more things to come!
-    """
-    _patch_error_handling(_ERROR_HANDLERS, _PatchedContainer.error_handler)
-    _patch_error_handling(_ERRORS_COPIERS, _PatchedContainer.copy_handler)
-
-
-def _patch_error_handling(methods, patch_handler) -> None:
-    for container in _PatchedContainer.containers_to_patch():
-        for method in methods:
-            original = getattr(container, method, None)
-            if original:
-                setattr(container, method, patch_handler(original))
-
-
 def _trace_function(
     trace_type: _ReturnsResultType,
     function_to_search: _FunctionType,
@@ -166,65 +109,107 @@ def _trace_function(
                 raise _DesiredFunctionFound()
 
 
-@final
-class _PatchedContainer(object):
-    """Class with helper methods to patched containers."""
-
-    __slots__ = ()
-
-    @classmethod
-    def containers_to_patch(cls) -> tuple:
-        """We need this method so coverage will work correctly."""
-        from returns.context import (
-            RequiresContextFutureResult,
-            RequiresContextIOResult,
-            RequiresContextResult,
-        )
-        from returns.future import FutureResult
-        from returns.io import IOFailure, IOSuccess
-        from returns.result import Failure, Success
-
-        return (
-            Success,
-            Failure,
-            IOSuccess,
-            IOFailure,
-            RequiresContextResult,
-            RequiresContextIOResult,
-            RequiresContextFutureResult,
-            FutureResult,
-        )
+class _DesiredFunctionFound(BaseException):  # noqa: WPS418
+    """Exception to raise when expected function is found."""
 
-    @classmethod
-    def error_handler(cls, original):
-        if inspect.iscoroutinefunction(original):
-            async def factory(self, *args, **kwargs):
-                original_result = await original(self, *args, **kwargs)
-                _ERRORS_HANDLED[id(original_result)] = original_result
-                return original_result
-        else:
-            def factory(self, *args, **kwargs):
-                original_result = original(self, *args, **kwargs)
-                _ERRORS_HANDLED[id(original_result)] = original_result
-                return original_result
-        return wraps(original)(factory)
-
-    @classmethod
-    def copy_handler(cls, original):
-        if inspect.iscoroutinefunction(original):
-            async def factory(self, *args, **kwargs):
-                original_result = await original(self, *args, **kwargs)
-                if id(self) in _ERRORS_HANDLED:
-                    _ERRORS_HANDLED[id(original_result)] = original_result
-                return original_result
-        else:
-            def factory(self, *args, **kwargs):
-                original_result = original(self, *args, **kwargs)
-                if id(self) in _ERRORS_HANDLED:
-                    _ERRORS_HANDLED[id(original_result)] = original_result
-                return original_result
-        return wraps(original)(factory)
 
+def pytest_configure(config) -> None:
+    """
+    Hook to be executed on import.
 
-class _DesiredFunctionFound(BaseException):  # noqa: WPS418
-    """Exception to raise when expected function is found."""
+    We use it define custom markers.
+    """
+    config.addinivalue_line(
+        'markers',
+        (
+            'returns_lawful: all tests under `check_all_laws` ' +
+            'is marked this way, ' +
+            'use `-m "not returns_lawful"` to skip them.'
+        ),
+    )
+
+
+@pytest.fixture()
+def returns() -> Iterator[ReturnsAsserts]:
+    """Returns class with helpers assertions to check containers."""
+    with _spy_error_handling() as errors_handled:
+        yield ReturnsAsserts(errors_handled)
+
+
+@contextmanager
+def _spy_error_handling() -> Iterator[_ErrorsHandled]:
+    """Track error handling of containers."""
+    errs: _ErrorsHandled = {}
+    with ExitStack() as cleanup:
+        for container in _containers_to_patch():
+            for method, patch in _ERROR_HANDLING_PATCHERS.items():
+                cleanup.enter_context(mock.patch.object(
+                    container,
+                    method,
+                    patch(getattr(container, method), errs=errs),
+                ))
+        yield errs
+
+
+# delayed imports are needed to prevent messing up coverage
+def _containers_to_patch() -> tuple:
+    from returns.context import (
+        RequiresContextFutureResult,
+        RequiresContextIOResult,
+        RequiresContextResult,
+    )
+    from returns.future import FutureResult
+    from returns.io import IOFailure, IOSuccess
+    from returns.result import Failure, Success
+
+    return (
+        Success,
+        Failure,
+        IOSuccess,
+        IOFailure,
+        RequiresContextResult,
+        RequiresContextIOResult,
+        RequiresContextFutureResult,
+        FutureResult,
+    )
+
+
+def _patched_error_handler(
+    original: _FunctionType, errs: _ErrorsHandled,
+) -> _FunctionType:
+    if inspect.iscoroutinefunction(original):
+        async def wrapper(self, *args, **kwargs):
+            original_result = await original(self, *args, **kwargs)
+            errs[id(original_result)] = original_result
+            return original_result
+    else:
+        def wrapper(self, *args, **kwargs):
+            original_result = original(self, *args, **kwargs)
+            errs[id(original_result)] = original_result
+            return original_result
+    return wraps(original)(wrapper)  # type: ignore
+
+
+def _patched_error_copier(
+    original: _FunctionType, errs: _ErrorsHandled,
+) -> _FunctionType:
+    if inspect.iscoroutinefunction(original):
+        async def wrapper(self, *args, **kwargs):
+            original_result = await original(self, *args, **kwargs)
+            if id(self) in errs:
+                errs[id(original_result)] = original_result
+            return original_result
+    else:
+        def wrapper(self, *args, **kwargs):
+            original_result = original(self, *args, **kwargs)
+            if id(self) in errs:
+                errs[id(original_result)] = original_result
+            return original_result
+    return wraps(original)(wrapper)  # type: ignore
+
+
+_ERROR_HANDLING_PATCHERS: Final = MappingProxyType({
+    'lash': _patched_error_handler,
+    'map': _patched_error_copier,
+    'alt': _patched_error_copier,
+})

tests/test_contrib/test_pytest/test_plugin_error_handler.py

@@ -6,7 +6,6 @@
     RequiresContextResult,
 )
 from returns.contrib.pytest import ReturnsAsserts
-from returns.contrib.pytest.plugin import _ERRORS_HANDLED
 from returns.functions import identity
 from returns.future import FutureResult
 from returns.io import IOFailure, IOSuccess
@@ -42,13 +41,15 @@ def _under_test(
 ])
 def test_error_handled(returns: ReturnsAsserts, container, kwargs):
     """Demo on how to use ``pytest`` helpers to work with error handling."""
-    assert not _ERRORS_HANDLED
+    assert not returns._errors_handled  # noqa: WPS437
     error_handled = _under_test(container, **kwargs)
 
     assert returns.is_error_handled(error_handled)
     assert returns.is_error_handled(error_handled.map(identity))
     assert returns.is_error_handled(error_handled.alt(identity))
 
+    assert returns._errors_handled  # noqa: WPS437
+
 
 @pytest.mark.parametrize('container', [
     Success(1),
@@ -64,14 +65,16 @@ def test_error_handled(returns: ReturnsAsserts, container, kwargs):
 ])
 def test_error_not_handled(returns: ReturnsAsserts, container):
     """Demo on how to use ``pytest`` helpers to work with error handling."""
-    assert not _ERRORS_HANDLED
+    assert not returns._errors_handled  # noqa: WPS437
     error_handled = _under_test(container)
 
     assert not returns.is_error_handled(container)
     assert not returns.is_error_handled(error_handled)
     assert not returns.is_error_handled(error_handled.map(identity))
     assert not returns.is_error_handled(error_handled.alt(identity))
 
+    assert not returns._errors_handled  # noqa: WPS437
+
 
 @pytest.mark.anyio()
 @pytest.mark.parametrize('container', [