# AssertionError: Expected 'foo' to be called with (1,) but was called with (2,)

- **ID:** `python/unittest-mock-side-effect-assertion-error`
- **Domain:** python
- **Category:** runtime_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The mock's call arguments don't match the expected arguments, often due to incorrect input or mock configuration.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (90% success)
   ```
   print(mock.call_args)
assert mock.call_args == call(1,)
   ```
2. **** (85% success)
   ```
   mock.assert_any_call(1)
   ```

## Dead Ends

- **** — This hides the real bug in the code. (80% fail)
- **** — It still fails if arguments don't match. (90% fail)