def METHOD_NAME(tmpdir):
    jupytext_py = tmpdir.join("jupytext.py")
    jupytext_py.write("# Not a config file!")
    assert find_jupytext_configuration_file(str(tmpdir)) is None
    dot_jupytext_py = tmpdir.join(".jupytext.py")
    dot_jupytext_py.write("# This is a config file!")
    assert find_jupytext_configuration_file(str(tmpdir)) == str(dot_jupytext_py)