def result(self) -> TResult:
        """The return value of the call, if it didn't raise.

        Can only be accessed if excinfo is None.
        """
        if self.excinfo is not None:
            raise AttributeError(f"{self!r} has no valid result")
        # The cast is safe because an exception wasn't raised, hence
        # _result has the expected function return type (which may be
        #  None, that's why a cast and not an assert).
        return cast(TResult, self._result)
The return value of the call, if it didn't raise.

        Can only be accessed if excinfo is None.
        
src/_pytest/runner.py