Test runner can't run in watch mode

[meisekimiu]

• Summary
  The test runner we're using can't run in watch mode since it requires a build to run the tests, and isn't configured to re-build when it re-runs tests. This means that it's basically pointless to run in test-watching mode. Also this means you can't simply run the test command through npx, and instead you need to make sure to build the application so the test runner can run the newest compiled version of the application.

• Other information (e.g. detailed explanation, stack traces, related issues, suggestions how to fix, links for us to have context, eg. StackOverflow, personal fork, etc.)
  Let's either configure the test runner to compile automatically every time it's run, or if that's not possible or too difficult, see about switching to another test runner.