test: add initial integration test suite

[agilgur5]

Summary

Creates a test harness/structure for integration tests and adds an initial integration test suite to it

• Gets a good way into the implementation of one of the longest-standing issues, lack of integration testing! Resolves one of the big leftover issues from https://github.com/ezolenko/rollup-plugin-typescript2/pull/311#issuecomment-1145551324
• Follow-up to #321

Details

• some additional ts-jest config is needed to parse index.ts

  • since Rollup isn't used when importing files during testing, we need to enable esModuleInterop
  • the import of findCacheDir was immediately erroring without this (and maybe more, but esModuleInterop made the import work)
  • add tsconfig.test.json for this purpose
  • use ts-jest JSDoc types to get types for the ts-jest config as well

• add an integration/ dir in the __tests__/ dir for all integration tests

  • add a fixtures/ dir in there as well for integration test fixtures
  • add a tsconfig.json for all fixtures to use
    • basically so that rpt2 source code is not included, though also bc this may be good to customize for fixtures
  • add a simple fixture with "no-errors" that does an import and a type-only import

• add a simple integration test that just ensures that all files are part of the bundle

  • the bundled index file and each file's declaration and declaration map
  • and no other files!
  • for Rollup, need to use paths relative to the root of the whole project
  • probably because that is cwd when running jest from root
  • will probably abstract out helpers here in the future as the test suite grows
  • 70% coverage of index.ts with just this one test!

• update CONTRIBUTING.md now that an integration test exists

EDIT: added more tests below!

• properly test the cache (92% coverage)
• test w/ and w/o declarations + declaration maps
• test case of plain JS that rpt2 skips and Rollup reads, which still makes it into the bundle
• test allowJs + emitDeclarationOnly from #366
• test missing/non-existent tsconfig error
• test semantic and syntactic error
  • plus w/ check: false and abortOnError: false

Review Notes

Creating the harness itself was probably the biggest "mental" blocker for me (mostly in the number of unknowns to solve, but didn't end up being that complex). Now that this is created, I've already started adding more tests to it, namely for edge cases and error cases. Might add some to this PR pending when it gets merged, but otherwise will add those in additional PRs.

• ~Also I haven't quite figured out the error testing process for non-fatal errors yet, but I~ was able to roughly get #345 tested with this harness as well, which is one reason why I felt more confident in moving that to "ready for review"
  • EDIT: have testing for warnings now
• EDIT: added more tests in this PR as it has yet to be merged. and this creates a larger harness/structure for different types of tests too. I think only watch mode tests are missing now

[agilgur5]

I've added a handful more integration tests now, so this is now a proper integration test suite, and not just a simple one-test harness anymore. Edited the title and description of the PR to match.

Had to bump test timeouts a couple times since integration tests take a good bit longer, especially when comparing two builds against each other (e.g. for cache / no cache).

A few more areas to add tests to:

• [x] ~more tsconfig parsing / merging errors~
  • EDIT: See #397
• [x] ~syntax errors~ / emitSkipped
  • EDIT: added a syntax error test, but apparently this doesn't trigger emitSkipped... 🤔
  • Filed https://github.com/microsoft/TypeScript/issues/49790 to help figure out how emitSkipped actually works and how to trigger it
• [x] ~Rollup watch mode~
  • EDIT: See #386
• [x] ~allowJs / the new emitDeclarationOnly support from #366~
  • EDIT: added a test for emitDeclarationOnly
• [x] ~declarationMap sources check (for #221)~
  • EDIT: See #403
• [ ] cache invalidation / isDirty checks will get to 100% coverage of the cache
  • EDIT: added one in #386 unsuccessfully (see notes there)
• [ ] tslib checks for resolve / load hooks

But this PR is (still) ready to review/merge, those are extras and can be done in future PRs (same as the tests I added today on top of the simple harness from a week ago)

[ezolenko]

Awesome!