Replace our integration test helpers with MetaTesting.jl #58
Description
The helpers we use to test ReTestItems.runtests were adapted from similar helpers in ChainRulesTestUtils (JuliaDiff/ChainRulesTestUtils.jl#62) which Seth kindly moved to a new package: https://github.com/sethaxen/MetaTesting.jl
If that package offers the functionality we need, then we could switch to it and not have to maintain our own helpers... plus then we can test our testing package with test helpers that are tested, which would be just lovely, wouldn't it?
We'd need JuliaTesting/MetaTesting.jl#2 + JuliaTesting/MetaTesting.jl#3 :)
I'm sure PRs would be welcome over there (we'd probably just need to agree on names for these functions)