Added tests for load_overrides() in Artifacts.jl

[u7581147]

Fixes #48551
Continued from #51815
The load_overrides() method in Artifacts.jl has a large untested branch. This PR increases the test coverage for this method.

https://app.codecov.io/gh/JuliaLang/julia/blob/master/stdlib%2FArtifacts%2Fsrc%2FArtifacts.jl#L121

[KristofferC]

Nice work. Would it be better to create a temporary folder (mktemp) and set the DEPOT_PATH to that folder and create the override file inside there? Then the temp folder would automatically be deleted in the end and there isn't a need for any explicit teardown, you just have to restore DEPOT_PATH to what it was before?

[u7581147]

That's a great idea! I'll be working on that.

[u7581147]

OK, I think I know why the new commit fails. Apparently, I saved a file in my Virtual Machine but forgot to delete it, so my machine was the only one where the code runs.

[staticfloat]

Overall, looks great to me, thank you for increasing test coverage in this area! I had a few style notes that I made for the test implementation.

[staticfloat]

You can use the do-block form of mktempdir() to explicitly scope when the temporary directory gets deleted, otherwise it only gets deleted at Julia exit. Example:

mktempdir() do temp_dir
    ...
end

[staticfloat]

The old depot path can have multiple elements, so the most correct way to do this is to do:

old_depot_path = copy(DEPOT_PATH)
empty!(DEPOT_PATH)
push!(DEPOT_PATH, temp_dir)
try
    ...
finally
    empty!(DEPOT_PATH)
    append!(DEPOT_PATH, old_depot_path)
end

The try/finally is so that even if something goes horribly wrong, the depot path doesn't cause cascading failures for other tests within this same file that may still run.

[u7581147]

Thank you so much for your idea! Yes, making sure that DEPOT_PATH will be restored to the status quo in the event of a bug is definitely the best practice.

[staticfloat]

Thanks, @u7581147!