Closure tests use t0pdfset as underlying law
Created by: Zaharid
The closure test code is supposed to read from a key called fakepdf as documented here
https://docs.nnpdf.science/tutorials/closuretest.html?highlight=closure+tests#brief-background
however when the way the code actually works is by setting the t0 pdf as underlying law. That is done here:
this was probably not noticed as the two things are usually set to be the same, but does cause surprising results when not, and may have affected some studies.