def METHOD_NAME(self):
    """Test that the function accepts NaN values correctly. """
    self.u_href[1, 1] = np.nan  # Adds NaN value
    expected_out = np.array(
        [
            [RMDI, RMDI, RMDI, RMDI],
            [RMDI, np.nan, 1.08434, RMDI],
            [RMDI, 1.08434, 1.08434, RMDI],
            [RMDI, RMDI, RMDI, RMDI],
        ]
    )
    result = FrictionVelocity(
        self.u_href, self.h_ref, self.z_0, self.mask
    ).process()
    self.assertIsInstance(result, np.ndarray)
    self.assertArrayAlmostEqual(result, expected_out)