White furnace test is basically a lighting integral against a constant white environment. White furnace test implementation for a few DSPBR https://github.com/DassaultSystemes-Technology/EnterprisePBRShadingModel models.
More info: Eric Heitz - "Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs", JCGT 2014 http://jcgt.org/published/0003/02/03/