Automated tests for JS modules

[bajtos]

Make it easy for module authors to write automated tests for their modules.

We need this functionality too for writing our internal tests for Zinnia JS APIs.

See https://deno.land/manual@v1.30.3/basics/testing

Features to consider:

• framework (API to define tests, test runner, test reporter)
  • collect test files
  • register all test suites (describe) and tests (it)
  • execute the tests
  • report test results
• CLI, e.g zinnia test
• Documentation for module authors.
• Unit-testing vs integration testing.
• Usability features
  • Run only a subset of tests
    • All tests in a single file (mocha test/file.js)
    • All tests matching a pattern (mocha -g regex)
    • Skip tests (it.skip and describe.skip)
    • Run only tests selected in code (it.only)

See https://deno.land/manual@v1.30.3/basics/testing for inspiration.

A Mastodon thread about DX aspects of JS testing frameworks: https://mastodon.social/@jamesshore@mastodon.online/110345771809205197

Out of scope

• Assertion library - people can bundle & vendor e.g. https://deno.land/std@0.177.0/testing/asserts.ts
• Code coverage
• Test runner CLI - zinnia test #215
• Test timeouts #214

Subtasks

• feat: a minimal testing framework #212
• Relax import sandboxing to allow a nested test file to access all production files
  feat: zinnia CLI can import JS from anywhere #218
  refactor: cleanup code handling import sandboxing #220
• Embed assert module again, this time as zinnia:assert
  feat: embed Deno assertions as zinnia:assert #217
• Write documentation for module authors
  docs: testing guide for module authors #222
• Use format_test_error from Deno's cli/tools.rs to get nicer error stack traces
  feat: prettify test failures #223

Estimate: Time-boxed to 2-3 days