Fix test memory usage (and speed?)

[davidzwa]

Often when running tests (even more so with coverage or sqlite) the result can be a fatal Javascript heap out of memory error. This is not a problem per se, given we can increase this heap. But its definitely a nuisance. Furthermore, tests are slow to run. I believe this can be improved.

Task description

• Investigate what the difference is between these scenarios
  • running a test without in-memory database
  • running a test with and without coverage
  • running a test without supertest and thus without server host
  • running an integration with and without awilix (Dependency Injection)
• Profile the CPU and memory usage of a unit test, service test, db+integration test and db+api test
• Commit these tests to a separate repository and create a follow-up issue to fire/report this on cron-based schedule
• If any improvement can be found in tests, for example by deduplicating SQLite instances, merging tests or reducing to reduction in test scope (skipping a awilix+host setup) do it.

Special note

There seems to be more memory/CPU usage when either running SQLite mode, or test coverage - my intuition says that coverage is the challenge here.