def METHOD_NAME(U):
    """
    Fraction whitcapping -- doesn't really check values
    but should catch gross errors!
    """
    print("testing for U:", U)
    w = Waves(test_wind_5, default_water)
    f = w.whitecap_fraction(U)
    assert f >= 0.0
    assert f <= 1.0
    if U == 4.0:
        # included the .5 factor from ADIOS2
        assert np.isclose(f, (0.05 / 3.85 / 2), rtol=1e-6)