def test_initailize_InitMassFromTotalMass():
data_arrays = mock_append_data_arrays(mass_array, num_elems)
substance = OilProps("oil_conservative")
spill = Spill(Release(datetime.now()))
spill.release.num_elements = 10
spill.set_mass(num_elems, units="g")
fcn = InitMassFromTotalMass()
fcn.initialize(num_elems, spill, data_arrays, substance)
assert_dataarray_shape_size(mass_array, data_arrays, num_elems)
assert np.all(1.0 == data_arrays["mass"])
