def METHOD_NAME():
    # See comment in test_expand_dmd_codelist_no_categories.
    mapping = [
        ("A2", "A1"),
        ("A2", "A0"),
        ("A1", "A0"),
        ("B2", "B1"),
        ("B2", "B0"),
        ("B1", "B0"),
        ("C2", "C1"),
        ("C2", "C0"),
        ("C1", "C0"),
    ]
    cl = codelist([("A0", "A"), ("B1", "B"), ("C2", "C"), ("D", "D")], "snomed")
    cl1 = expand_dmd_codelist(cl, mapping)
    assert list(cl1) == [
        ("A0", "A"),
        ("A1", "A"),
        ("A2", "A"),
        ("B0", "B"),
        ("B1", "B"),
        ("B2", "B"),
        ("C0", "C"),
        ("C1", "C"),
        ("C2", "C"),
        ("D", "D"),
    ]
    assert cl1.system == "snomed"