def addinivalue_line(self, name: str, line: str) -> None:
        """Add a line to an ini-file option. The option must have been
        declared but might not yet be set in which case the line becomes
        the first line in its value."""
        x = self.getini(name)
        assert isinstance(x, list)
        x.append(line)  # modifies the cached list inline
Add a line to an ini-file option. The option must have been
        declared but might not yet be set in which case the line becomes
        the first line in its value.
src/_pytest/config/__init__.py