Test: Add @include_files for filtering test files

[IanButterworth]

Formalizes a way to select test files at the Pkg.test level.

i.e. runtests.jl

using Test

include("utils.jl") # common utils

@include_files [
    "foo.jl",
    "bar.jl",
    "baz.jl",
]

Then to run tests use --files (which matches files using occursin)

Pkg.test(test_args=["--files=foo"])

or using --files-regex for regex matching

Pkg.test(test_args=["--files-regex=foo|bar"])

More examples in the docstring.

Backwards compat provided via Compat.jl JuliaLang/Compat.jl#846

---

This is largely inspired by Claude constantly expecting this to work:

Pkg.test(test_args=["file_name"]) 

However I required the --files or --files-regex arg name because otherwise what Claude wanted would restrict any other usage of test_args/ARGS

[vchuravy]

I am personally not a big fan of having to enumerate test files and prefer ParallelTestRunner.jl style of auto discovery and filtering.

Also is there a strong reason why this must be in Test.jl? I do think that separating the declaration of tests from the running and execution of tests is a good thing.

[IanButterworth]

It's true that it could be in Base, that didn't occur to me.

What's stopping putting ParallelTestRunner into Base/Test?

[vchuravy]

ParallelTestRunner into Base/Test?

Mostly because we are rapidly iterating on functionality, and until Test is upgradeable, I don't feel like waiting for new features.

Also ParallelTestRunner uses Malt.jl (but could use Distributed again, or hand role it's own worker management)