fix(spy): ensure class signature uses __call__ (#120)

Author: mcous

decoy/spec.py

@@ -71,8 +71,10 @@ def get_full_name(self) -> str:
 
     def get_signature(self) -> Optional[inspect.Signature]:
         """Get the Spec's signature, if Spec represents a callable."""
+        source = self._get_source()
+
         try:
-            return inspect.signature(self._source)  # type: ignore[arg-type]
+            return inspect.signature(source)
         except TypeError:
             return None
 
@@ -82,18 +84,12 @@ def get_class_type(self) -> Optional[Type[Any]]:
 
     def get_is_async(self) -> bool:
         """Get whether the Spec represents an async. callable."""
-        source = self._source
+        source = self._get_source()
 
         # `iscoroutinefunction` does not work for `partial` on Python < 3.8
         if isinstance(source, functools.partial):
             source = source.func
 
-        # check if spec source is a class with a __call__ method
-        elif inspect.isclass(source):
-            call_method = inspect.getattr_static(source, "__call__", None)
-            if inspect.isfunction(call_method):
-                source = call_method
-
         return inspect.iscoroutinefunction(source)
 
     def bind_args(self, *args: Any, **kwargs: Any) -> BoundArgs:
@@ -141,6 +137,19 @@ def get_child_spec(self, name: str) -> "Spec":
 
         return Spec(source=child_source, name=child_name, module_name=self._module_name)
 
+    def _get_source(self) -> Any:
+        source = self._source
+
+        # check if spec source is a class with a __call__ method
+        if inspect.isclass(source):
+            call_method = inspect.getattr_static(source, "__call__", None)
+            if inspect.isfunction(call_method):
+                # consume the `self` argument of the method to ensure proper
+                # signature reporting by wrapping it in a partial
+                source = functools.partial(call_method, None)
+
+        return source
+
 
 def _get_type_hints(obj: Any) -> Dict[str, Any]:
     """Get type hints for an object, if possible.

tests/common.py

@@ -57,7 +57,15 @@ async def do_the_thing(self, *, flag: bool) -> None:
 class SomeAsyncCallableClass:
     """Async callable class."""
 
-    async def __call__(self) -> int:
+    async def __call__(self, val: int) -> int:
+        """Get an integer."""
+        ...
+
+
+class SomeCallableClass:
+    """Async callable class."""
+
+    async def __call__(self, val: int) -> int:
         """Get an integer."""
         ...
 

tests/test_spec.py

@@ -9,6 +9,7 @@
     SomeClass,
     SomeAsyncClass,
     SomeAsyncCallableClass,
+    SomeCallableClass,
     SomeNestedClass,
     some_func,
     some_async_func,
@@ -164,6 +165,19 @@ class GetSignatureSpec(NamedTuple):
                 return_annotation=int,
             ),
         ),
+        GetSignatureSpec(
+            subject=Spec(source=SomeCallableClass, name=None),
+            expected_signature=inspect.Signature(
+                parameters=[
+                    inspect.Parameter(
+                        name="val",
+                        kind=inspect.Parameter.POSITIONAL_OR_KEYWORD,
+                        annotation=int,
+                    )
+                ],
+                return_annotation=int,
+            ),
+        ),
     ],
 )
 def test_get_signature(