Making TestImplementation available for the whole framework

[szabo137]

Since the TestImplementations module from #98 could be of use for other packages in the framework, we should make it available.

Requirements

The TestImplementations module should

• not be a standalone package (too much maintenance overhead for just a test implementation;)
• should be accessible for all other packages in the framework
• be placed somewhat near to QEDbase.jl (it is tightly bounded and will probably updated only with QEDbase.jl)

Suggested solution

Maybe we should try to register the TestImplementation as a subdir-package, as discussed here and here.

Other examples, where this is established:

• BenchmarkPlots in BenchmarkTools.jl
• InlineTest in ReTest.jl

Final thoughts and open questions

When establishing this, one could also try to include some documentation for TestImplementation into the QEDbase docs.
However, there are still some open questions:

• Can we use the TagBot?
• Do we need to think about integration tests?
• are there any points we need to discuss regarding our current development/test/release workflow?

[szabo137]

As we discussed offline: the proposed way would introduce circular test-dependencies again. Therefore, we should rather add the TestImplementation module directly to QEDbase.jl as a submodule. Then we could just write

using QEDbase.tests

proc = TestProcess(2,3)

After the next release of QEDbase.jl, this would also be available for the other packages in the framework.
Another benefit would be, that the test implementations could also go to the same test pipelines as QEDbase, which is especially nice for integration tests.