# PytestUnknownMarkWarning: Unknown pytest.mark.slow - is this a typo? You can register it with markers option

- **ID:** `python/pytest-marker-unknown`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A custom marker is used in tests but not registered in pytest configuration, causing a warning during collection.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.8 | active | — | — |
| 3.9 | active | — | — |
| 3.10 | active | — | — |
| 3.11 | active | — | — |
| 3.12 | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   Register the marker in pytest.ini: `[pytest]
markers =
    slow: marks tests as slow`
   ```
2. **** (90% success)
   ```
   Use `pytest --markers` to list all registered markers and ensure the custom one is defined.
   ```

## Dead Ends

- **** — This removes useful metadata for test selection and organization. (80% fail)
- **** — The warning may escalate to an error in future pytest versions, and it hides potential typos. (60% fail)