Resolve "Unit tests coverage: Enable Karma Coverage"

Closes #1287 (closed)

Background (for future reference)

This didn't work out of the box because we don't have our component files in app/src, as is the norm for Angular projects. We have them in lib and I had to change sourceRoot in angular.json accordingly, because as it turns out this is where Karma (or karma-coverage?) looks for spec files (see here). The code coverage computation seems to not take into consideration the path specified in angular.json under "test" (this can actually be removed now that I changed sourceRoot).

There might be other ways to include files in the coverage computation (like file parameter in karma config or ng test --include, maybe also parameters in the karma config), but none of them did anything for me.

This doesn't seem to affect any other parts of the pipeline, I was still able to build the app normally. I also couldn't find anything about what else sourceRoot is actually used for in the docs.

I made it so that the code coverage is computed on each run. We can turn that off again with "codeCoverage": false in angular.json, then we'd have to call it explicitly with ng test --code-coverage

Testing

Run yarn install to install the new dependency, then run ng test.

Output (after 480 tests):

=============================== Coverage summary ===============================
Statements   : 35.48% ( 2986/8414 )
Branches     : 22.64% ( 536/2367 )
Functions    : 26.99% ( 711/2634 )
Lines        : 35.84% ( 2657/7412 )
================================================================================

It also creates/updates the ./coverage directory (not part of the git repo). You can open the index.html in your browser and see the test coverage for each component.