## TL;DR
Import `xdist`, not `pytest_xdist`. The package is called `pytest-xdist` on PyPI but the importable module is just `xdist`. If you actually need the plugin, `pip install pytest-xdist` is the fix.

```text
ModuleNotFoundError: No module named 'pytest_xdist'
```

## Fix it

1. **Fix the import.** Change `import pytest_xdist` to `import xdist`.
   - Expected: the import succeeds (if pytest-xdist is installed).

2. **If it still fails**, install the package: `python -m pip install pytest-xdist`.
   - Expected: `Successfully installed pytest-xdist-...`.

## When this applies
- You guessed the module name from the PyPI package name.
- Code or docs you copied use the wrong import.

## When it does not apply
- If `import xdist` also fails, the package is genuinely not installed.

## Tool compatibility
pytest-xdist 2.x/3.x. The module has always been `xdist`.

## Why it happens
PyPI package names and import names often differ. The `pytest-` prefix is a naming convention for plugins; the module drops it.

## Edge cases
- Same trap as `pytest-cov` (module `pytest_cov`, which keeps the prefix) versus `pytest-xdist` (module `xdist`, which drops it). Check each plugin's docs.