Move AbstractGPs related test from GPLikelihoods here

[theogf]

I removed the tests using AbstactGPs from GPLikelihoods and saved them in this gist. They should probably be added here (or ApproximateGPs) to check compatibility.

[willtebbutt]

I think I would prefer ApproximateGPs, but just because we already have this as a dependency there. I could be convinced otherwise.

[theogf]

I really don't mind either, but somehow I think these tests could still fit GPLikelihoods just not in the interface module.

[willtebbutt]

Sorry, I'm not sure what you mean. Could you elaborate?

[theogf]

Well the whole point of GPLikelihoods is to work together with the rest of the ecosystem. So I think we should know when changes in GPLikelihoods might be incompatible with AppGP or AbsGP.

[willtebbutt]

Fair point. Taking another look at the code, it looks like it would be fine in this package (I was worried we'd need some of the code in ApproximateGPs in order to run decent tests, but the ones that we currently have seem fine without it).

Where were you thinking to locate these tests? test or src?

[theogf]

Definitely test right now GPLikelihoods is not a dependency and that would not make sense to add it.

[willtebbutt]

Cool. I'm very happy to review if you open a PR.

[st--]

What's the reason for not just having this within the GPLikelihoods package ?

[theogf]

You mean in the tests of GPLikelihoods?