Move test dependencies from [extras], [targets] to their own .toml files.

[nathanrboyer]

Pkg documentation says test dependencies after Julia 1.2 should use their own environment, but PkgTemplates does not create the files this way.

[bicycle1885]

I guess what you want is Tests(project = true). See https://invenia.github.io/PkgTemplates.jl/stable/user/#PkgTemplates.Tests.

[nickrobinson251]

Yes, this feature is available via Tests(project=true) :)

We haven't change the default from Tests(project=false) as in our experience (at Invenia) it is actually more difficult maintaining test dependencies when in a separate test/Project.toml, and from what i can see in the ecosystem test/Project.toml hasn't generally become the default.