[WIP] [do not review] single-module tester

[timotheecour]

No description provided.

[krux02]

I have a suggestion, use when defined(testing),then you can run the tests with nim c -r -d:testing test_all.nim

[timotheecour]

I have a suggestion, use when defined(testing),then you can run the tests with nim c -r -d:testing test_all.nim

ya, that was my intention but slightly different, see #9581 (comment)

replace when isMainModule blocks by when isMainModule or defined(testing) for all files we want to test in testament

[Araq]

This is now covered by the "megatest" category in testament.