Start migration of tests to electron-mocha

[araujoarthur0]

Related issue

Helps #1037

Context / Background

Refer to #1054. Here I'm starting to migrate our tests to the electron-mocha infrastructure, which works well with ES6 modules. I think I'll only be able to pre-migrate the ones that don't depend on jest-specific things, before switching fully to ES6. Starting with the simple test tests/main/time-math.js as an example here.

What change is being introduced by this PR?

• Dependency changes
  • @babel/plugin-transform-modules-commonjs is used to convert ES6 into common js while we don't move fully to ES6.
  • electron-mocha and mocha will be the test runners we use
  • Added c8 dependency, which has the same purpose as nyc, that of a code coverage runner around mocha. Had to use this one because nyc doesn't work with electron-mocha. Anyway, c8 is considered the native replacement to nyc, and the output is exactly the same.
• Added config files for electron-mocha. Some configs like color and parallel are to make the test runs better.
• Added new npm target "test:electron-mocha-main", which is used in the test pipeline.
• Migrated time-math.js test to use mocha.
  • Removed time-math.js from the jest matching tests, now that it's migrated.
  • Added it to electron-mocha-main.config.js

How will this be tested?

Pipeline passes in the same way, coverage will be coming from two reports and is currently being merged into a single report. CodeCov is properly parsing the combination.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (8f2ae80) 80.00% compared to head (9b9c47b) 81.37%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1061 +/- ## ========================================== + Coverage 80.00% 81.37% +1.37% ========================================== Files 20 22 +2 Lines 1270 1401 +131 Branches 191 214 +23 ========================================== + Hits 1016 1140 +124 - Misses 254 261 +7 ```

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[araujoarthur0]

Seems fine, actually easier than I thought, dependency changes aside, but I think that's because time-math has no stubs/mocks, right?

Yes, I chose the simplest one to get it along with the infrastructure changes 🤣