def METHOD_NAME(variants_vec_backends_once_rgb):
    # spec_trans inside (wi.z() < 0)
    xml = """<float name="roughness" value="0.5"/>
             <float name="anisotropic" value="0.4"/>
             <float name="clearcoat" value="0.8"/>
             <float name="spec_trans" value="0.7"/>
             <float name="eta" value="1.5"/>
          """
    wi = dr.normalize(mi.ScalarVector3f([1, 0, -1]))
    sample_func, pdf_func = mi.chi2.BSDFAdapter("principled", xml, wi=wi)
    chi2 = mi.chi2.ChiSquareTest(
        domain=mi.chi2.SphericalDomain(),
        sample_func=sample_func,
        pdf_func=pdf_func,
        sample_dim=3
    )
    assert chi2.run()