def METHOD_NAME(IOtest_mtz):
    """Test rs.read_mtz() with merged MTZ file"""
    dataset = rs.read_mtz(IOtest_mtz)
    assert dataset.spacegroup.number == 96
    assert dataset.columns.to_list() == ["FMODEL", "PHIFMODEL"]
    assert dataset.index.names == ["H", "K", "L"]
    assert isinstance(dataset, rs.DataSet)