def METHOD_NAME(self):
    col = Collection()
    col.songs = (AudioFile({'~#length': 30}), AudioFile({'~#length': 210}))
    min_length = NumexprTag('length:min')
    max_length = NumexprTag('length:max')
    avg_length = NumexprTag('length:avg')
    assert Numcmp(min_length, ">", numexprUnit(10, "seconds"))
    assert Numcmp(min_length, "<", numexprUnit(2, "minutes"))
    assert Numcmp(max_length, "<", numexprUnit(1, "hour"))
    assert Numcmp(max_length, ">=", numexprUnit(30, "seconds"))
    assert Numcmp(avg_length, "=", numexprUnit(2, "minutes"))