def METHOD_NAME(tmpdir, dummy_molecule):
    """
    Test that the header is written.
    """
    header = (
        'This is a header.',
        'It contains more than one line.',
    )
    expected = (
        '; This is a header.\n',
        '; It contains more than one line.\n',
        '\n',
    )
    outpath = tmpdir / 'out.itp'
    with open(str(outpath), 'w') as outfile:
        write_molecule_itp(dummy_molecule, outfile, header=header)
    with open(str(outpath)) as infile:
        for line, expected_line in zip(infile, expected):
            assert line == expected_line