Configure Jest

[zainfathoni]

Background

Thanks to our fellow contributors, we managed to work for multiple streams in parallel.
Unfortunately, our end-to-end test cannot test the upstream works without the downstream elements implemented, e.g. it couldn't test the database schema and operations without the form implementation.

Therefore, It's time to introduce a proper unit and integration tests infrastructure.

Implementation Model

You can refer to this PR as an example: kawalcovid19/wargabantuwarga.com#358.

Tasks

• Install & configure jest, testing-library, and @jackfranklin/test-data-bot libraries
  • Jest as a test runner
  • Testing Library family of libraries as React test renderers
  • @jackfranklin/test-data-bot as a mock data generator to signal the relationships between values in our tests
• Run only relevant Jest Tests on Git pre-commit hooks
• Configure code coverage collections and threshold
• Separate client and server Jest configurations
• Add unit test scripts
  • test:watch for running tests while watching changed files
  • test:coverage for running all tests and gather the test coverage
  • test:debug for debugging unit tests