# AssertionError: Arrays are not equal (mismatch 100.0%) x: array([nan]) y: array([nan])

- **ID:** `python/numpy-nan-comparison`
- **Domain:** python
- **Category:** data_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

np.testing.assert_array_equal treats NaN == NaN as False by default. Also affects boolean masks built from NaN comparisons.

## Version Compatibility

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

## Workarounds

1. **** (95% success)
   ```
   np.testing.assert_array_equal(a, b, strict=False) or use np.testing.assert_allclose(a, b, equal_nan=True)
   ```
2. **** (90% success)
   ```
   mask = (a == b) | (np.isnan(a) & np.isnan(b)); assert mask.all()
   ```

## Dead Ends

- **** — Also returns False for NaN (90% fail)
- **** — NaN != NaN, returns False (90% fail)