fix(matchers): ensure ErrorMatching return type matches spec (#86)

Author: mcous

decoy/matchers.py

@@ -24,7 +24,7 @@ def test_logger_called(decoy: Decoy):
     equality comparisons (`==`) for stubbing and verification.
 """
 from re import compile as compile_re
-from typing import cast, Any, List, Mapping, Optional, Pattern, Type
+from typing import cast, Any, List, Mapping, Optional, Pattern, Type, TypeVar
 
 
 __all__ = [
@@ -255,10 +255,10 @@ def StringMatching(match: str) -> str:
 
 
 class _ErrorMatching:
-    _error_type: Type[Exception]
+    _error_type: Type[BaseException]
     _string_matcher: Optional[_StringMatching]
 
-    def __init__(self, error: Type[Exception], match: Optional[str] = None) -> None:
+    def __init__(self, error: Type[BaseException], match: Optional[str] = None) -> None:
         """Initialize with the Exception type and optional message matcher."""
         self._error_type = error
         self._string_matcher = _StringMatching(match) if match is not None else None
@@ -281,7 +281,10 @@ def __repr__(self) -> str:
         )
 
 
-def ErrorMatching(error: Type[Exception], match: Optional[str] = None) -> Exception:
+ErrorT = TypeVar("ErrorT", bound=BaseException)
+
+
+def ErrorMatching(error: Type[ErrorT], match: Optional[str] = None) -> ErrorT:
     """Match any error matching an Exception type and optional message matcher.
 
     Arguments:
@@ -294,7 +297,7 @@ def ErrorMatching(error: Type[Exception], match: Optional[str] = None) -> Except
         assert ValueError("oh no!") == ErrorMatching(ValueError, match="no")
         ```
     """
-    return cast(Exception, _ErrorMatching(error, match))
+    return cast(ErrorT, _ErrorMatching(error, match))
 
 
 class _Captor:

tests/test_matchers.py

@@ -95,7 +95,7 @@ def test_error_matching_matcher() -> None:
     """It should have an "any error that matches" matcher."""
     assert RuntimeError("ah!") == matchers.ErrorMatching(RuntimeError)
     assert RuntimeError("ah!") == matchers.ErrorMatching(RuntimeError, "ah")
-    assert RuntimeError("ah!") != matchers.ErrorMatching(TypeError, "ah")
+    assert RuntimeError("ah!") != matchers.ErrorMatching(TypeError, "ah")  # type: ignore[comparison-overlap]  # noqa: E501
     assert RuntimeError("ah!") != matchers.ErrorMatching(RuntimeError, "ah$")
 
 

tests/typing/test_typing.yml

@@ -130,5 +130,5 @@
       main:4: note: Revealed type is "Any"
       main:5: note: Revealed type is "Any"
       main:6: note: Revealed type is "builtins.str"
-      main:7: note: Revealed type is "builtins.Exception"
+      main:7: note: Revealed type is "builtins.RuntimeError*"
       main:8: note: Revealed type is "Any"