def METHOD_NAME(self):
    # Make sure it works with zero mean (pure second moment).
    zero_coeff = np.zeros((self.basis.count,), dtype=self.dtype)
    covar_cov2d = self.cov2d.get_covar(
        self.coeff, mean_coeff=zero_coeff, ctf_fb=self.ctf_fb, ctf_idx=self.ctf_idx
    )
    covar_bcov2d = self.bcov2d.get_covar(mean_coeff=zero_coeff)
    self.assertTrue(
        self.blk_diag_allclose(
            covar_cov2d, covar_bcov2d, atol=utest_tolerance(self.dtype)
        )
    )