def METHOD_NAME(variants_vec_backends_once_rgb):
    # back side thin
    xml = """<float name="roughness" value="0.6"/>
             <float name="anisotropic" value="0.5"/>
             <float name="spec_trans" value="0.6"/>
             <float name="eta" value="1.3296"/>
             <float name="diff_trans" value="0.9"/>
        """
    wi = dr.normalize(mi.ScalarVector3f([1, 0, -1]))
    sample_func, pdf_func = mi.chi2.BSDFAdapter("principledthin", 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()