feat(verify): add proper assertion messages (#7)

Closes #4

Author: mcous

decoy/__init__.py

@@ -1,5 +1,6 @@
 """Decoy test double stubbing and verification library."""
-from typing import cast, Any, Optional, Type
+from os import linesep
+from typing import cast, Any, Optional, Sequence, Type
 
 from .registry import Registry
 from .spy import create_spy, SpyCall
@@ -139,8 +140,9 @@ def test_create_something(decoy: Decoy):
             call stack, which will end up being the call inside `verify`.
         """
         rehearsal = self._pop_last_rehearsal()
+        all_calls = self._registry.get_calls_by_spy_id(rehearsal.spy_id)
 
-        assert rehearsal in self._registry.get_calls_by_spy_id(rehearsal.spy_id)
+        assert rehearsal in all_calls, self._build_verify_error(rehearsal, all_calls)
 
     def _pop_last_rehearsal(self) -> SpyCall:
         rehearsal = self._registry.pop_last_call()
@@ -160,3 +162,21 @@ def _handle_spy_call(self, call: SpyCall) -> Any:
                 return stub._act()
 
         return None
+
+    def _build_verify_error(
+        self, rehearsal: SpyCall, all_calls: Sequence[SpyCall]
+    ) -> str:
+        all_calls_len = len(all_calls)
+        all_calls_plural = all_calls_len != 1
+        all_calls_printout = linesep.join(
+            [f"{n + 1}.\t{str(all_calls[n])}" for n in range(all_calls_len)]
+        )
+
+        return linesep.join(
+            [
+                "Expected call:",
+                f"\t{str(rehearsal)}",
+                f"Found {all_calls_len} call{'s' if all_calls_plural else ''}:",
+                all_calls_printout,
+            ]
+        )

decoy/matchers.py

@@ -104,7 +104,7 @@ def __eq__(self, target: object) -> bool:
 
     def __repr__(self) -> str:
         """Return a string representation of the matcher."""
-        return f"<IsNot {self._reject_value}>"
+        return f"<IsNot {repr(self._reject_value)}>"
 
 
 def IsNot(value: object) -> Any:
@@ -138,7 +138,7 @@ def __eq__(self, target: object) -> bool:
 
     def __repr__(self) -> str:
         """Return a string representation of the matcher."""
-        return f"<StringMatching {self._pattern.pattern}>"
+        return f"<StringMatching {repr(self._pattern.pattern)}>"
 
 
 def StringMatching(match: str) -> str:

decoy/spy.py

@@ -6,7 +6,7 @@
 from __future__ import annotations
 from dataclasses import dataclass
 from inspect import isclass, iscoroutinefunction
-from typing import get_type_hints, Any, Callable, Dict, Optional, Tuple
+from typing import get_type_hints, Any, Callable, Dict, Optional, Tuple, Type
 
 
 @dataclass(frozen=True)
@@ -20,9 +20,21 @@ class SpyCall:
     """
 
     spy_id: int
+    spy_name: str
     args: Tuple[Any, ...]
     kwargs: Dict[str, Any]
 
+    def __str__(self) -> str:
+        """Stringify the call to something human readable.
+
+        `SpyCall(spy_id=42, spy_name="name", args=(1,), kwargs={"foo": False})`
+        would stringify as `"name(1, foo=False)"`
+        """
+        args_list = [repr(arg) for arg in self.args]
+        kwargs_list = [f"{key}={repr(val)}" for key, val in self.kwargs.items()]
+
+        return f"{self.spy_name}({', '.join(args_list + kwargs_list)})"
+
 
 CallHandler = Callable[[SpyCall], Any]
 
@@ -34,8 +46,14 @@ class BaseSpy:
     - Lazily constructs child spies when an attribute is accessed
     """
 
-    def __init__(self, handle_call: CallHandler, spec: Optional[Any] = None) -> None:
+    def __init__(
+        self,
+        handle_call: CallHandler,
+        spec: Optional[Any] = None,
+        name: Optional[str] = None,
+    ) -> None:
         """Initialize a BaseSpy from a call handler and an optional spec object."""
+        self._name = name or (spec.__name__ if spec is not None else "spy")
         self._spec = spec
         self._handle_call: CallHandler = handle_call
         self._spy_children: Dict[str, BaseSpy] = {}
@@ -73,6 +91,7 @@ def __getattr__(self, name: str) -> Any:
         spy = create_spy(
             handle_call=self._handle_call,
             spec=child_spec,
+            name=f"{self._name}.{name}",
         )
 
         self._spy_children[name] = spy
@@ -85,28 +104,31 @@ class Spy(BaseSpy):
 
     def __call__(self, *args: Any, **kwargs: Any) -> Any:
         """Handle a call to the spy."""
-        return self._handle_call(SpyCall(id(self), args, kwargs))
+        return self._handle_call(SpyCall(id(self), self._name, args, kwargs))
 
 
-class AsyncSpy(Spy):
+class AsyncSpy(BaseSpy):
     """An object that records all async. calls made to itself and its children."""
 
     async def __call__(self, *args: Any, **kwargs: Any) -> Any:
         """Handle a call to the spy asynchronously."""
-        return self._handle_call(SpyCall(id(self), args, kwargs))
+        return self._handle_call(SpyCall(id(self), self._name, args, kwargs))
 
 
 def create_spy(
     handle_call: CallHandler,
     spec: Optional[Any] = None,
     is_async: bool = False,
+    name: Optional[str] = None,
 ) -> Any:
     """Create a Spy from a spec.
 
     Functions and classes passed to `spec` will be inspected (and have any type
     annotations inspected) to ensure `AsyncSpy`'s are returned where necessary.
     """
+    _SpyCls: Type[BaseSpy] = Spy
+
     if iscoroutinefunction(spec) or is_async is True:
-        return AsyncSpy(handle_call)
+        _SpyCls = AsyncSpy
 
-    return Spy(handle_call=handle_call, spec=spec)
+    return _SpyCls(handle_call=handle_call, spec=spec, name=name)