(#325) Give spec to Mock so it throws when typo in assert

src/ophyd_async/core/mock_signal_backend.py

@@ -1,6 +1,6 @@
 import asyncio
 from functools import cached_property
-from typing import Optional, Type
+from typing import Callable, Optional, Type
 from unittest.mock import Mock
 
 from bluesky.protocols import Descriptor, Reading
@@ -47,7 +47,7 @@ async def connect(self, timeout: float = DEFAULT_TIMEOUT) -> None:
 
     @cached_property
     def put_mock(self) -> Mock:
-        return Mock(name="put")
+        return Mock(name="put", spec=Callable)
 
     @cached_property
     def put_proceeds(self) -> asyncio.Event:

tests/core/test_mock_signal_backend.py

@@ -352,3 +352,13 @@ async def set(self):
     assert await signal.get_value() == 0
     backend_put(100)
     assert await signal.get_value() == 100
+
+
+async def test_when_put_mock_called_with_typo_then_fails_but_calling_directly_passes():
+    mock_signal = SignalRW(SoftSignalBackend(int))
+    await mock_signal.connect(mock=True)
+    assert isinstance(mock_signal._backend, MockSignalBackend)
+    mock = mock_signal._backend.put_mock
+    with pytest.raises(AttributeError):
+        mock.asssert_called_once()  # Note typo here is deliberate!
+    mock()