first draft of alire test runner

[AldanTanneo]

This is a demo implementation of what a minimal Alire test runner could look like, following the proposed design in #1831.

For now, it only takes two arguments: a -j[obs=]N arg that specifies how many tests should be run in parallel (defaults to 0, aka how many cores your machine has) and --dir=<dir>, specifying which sub-directory holds your tests (defaults to tests).

To test it:

Have a repository with a tests folder containing a binary crate. In the GPR file, replace the Main setting with

for Main use [Crate_Name]_List_Config.Test_Files;

and at the top, add

with "config/[crate name]_list_config.gpr";

Each .adb file in src/ should contain a single main procedure. You can add extra source directories (like common...), they will not be considered test folders, and you can put extra test code in there, to be used from the actual test procedures.

A test fails when its exit code is not zero (for instance, from an unhandled exception).

Finally, simply run alr test2 with the alr from this branch.

[mosteo]

Thanks for providing this prototype, César. I'll play with it in the coming days.