def cls(self):
        """Class (can be None) where the test function was collected."""
        if self.scope not in ("class", "function"):
            raise AttributeError(f"cls not available in {self.scope}-scoped context")
        clscol = self._pyfuncitem.getparent(_pytest.python.Class)
        if clscol:
            return clscol.obj
Class (can be None) where the test function was collected.
src/_pytest/fixtures.py