human
I wrote the below code

    @contextlib.contextmanager
    def _mock(filename, mode):
        if (not (mode == 'w')):
            raise RuntimeError('unexpected    opening    mode    for    stringio_open')
        FILE_REGISTRY[filename] = StringIO()
        try:
            (yield FILE_REGISTRY[filename])
        finally:
            handle = FILE_REGISTRY[filename]
            FILE_REGISTRY[filename] = handle.getvalue()
            handle.close()
    monkeypatch.setattr(spack.modules, 'open', _mock, raising=False)

What's a good function header?
 Here's a good function header?
assistant
#Here's a good function header.

@pytest.fixture()
def stringio_open(monkeypatch):