Small tests for infinite partition function

[kshyatt]

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[leburgel]

Test failures seem unrelated, something in the Lorentzian broadening test for the SVD pullback. Anything we should worry about @pbrehmer?

[pbrehmer]

Test failures seem unrelated, something in the Lorentzian broadening test for the SVD pullback. Anything we should worry about @pbrehmer?

No this seems unproblematic. I would assume that since we now obtain more accurate gradients due to #276 some of the SVD gradient values have changed. In that particular test that fails, the unbroadened gradient is now slightly more accurate when there are degenerate singular values but it is still deviating from the broadened gradients significantly (i.e. suffers from the same problem of divergences). I will just need to lower the tolerance slightly to make this stable again; I'll do that in #270 since there we anyway need to think about the SVD broadening again.