PR Checklist

• Steps inContributing were taken

References:

• Enhancement: snapshot testing for lint rule failures #6499
• feat(utils): add dependency constraint filtering forRuleTester #5750
• Add automated regression testing against old TS versions #1752

Overview

The changes I implemented in#5750 were pretty complex to build because I was working around how the baseRuleTester class did things. I ran into a lot of weirdness due to things like the class expecting specific properties on objects.

In looking to implement#6499 - I don't want to hit the same issues, so I think it's best if we just draw a line in the sand and fork it so that we can build our enhancements directly into the tooling.

This is also good because it means that we can provide a new baseline for testing and don't need to worry about what the installed ESLint version supports - which will make our eventual dependency testing easier.

This PR:

• fork the base class and adds types
  • The logic itself is unchanged, but I did move some things around to make it a bit easier to type and manage.
• clones the base eslint test forRuleTester
  • This test is completely unchanged because it'll take a complete rewrite to make it jest-compatible.
• adds the changes we've added in our existing subclass fork:
  • addsafterAll as additional static "test framework providers" to the class.
  • adds a new per-test option -skip which runs the test usingit.skip.
  • adds automatic parser cache cleaning usingafterAll.
  • adds automatic file naming for type-aware linting
    • I implemented this slightly differently than before:
      • it uses a different default name fortsx files now
      • the default filenames can be overridden in the constructor (previously you HAD to do it per test).
  • adds per-test dependency constraints
    • I implemented this slightly differently than before:
      Before our hands were tied and I had to lean on settingonly on every test to filter out the skipped tests - now with the newskip functionality we only need setskip on these tests which is a much, much nicer implementation!
• adds new features
  • adds a new per-test option -skip which runs the test case usingit.skip.
  • addsitSkip anddescribeSkip as additional static "test framework providers" to the class.
  • adds a newdefaultFilenames constructor option to allow configuring the default filenames used for type-aware testing.

Documentation:
https://deploy-preview-6777--typescript-eslint.netlify.app/architecture/rule-tester

TODO:

• add a new package
• fork the base class
• implement the changes we have inour current subclass fork
  • implement automatic parser cache cleaning
  • implement automatic file naming for type-aware linting
  • implement the dependency checks fromfeat(utils): add dependency constraint filtering forRuleTester #5750
• migrate codebase to this ruletester
  • i'll do this in a separate PR
• implement snapshot testingEnhancement: snapshot testing for lint rule failures #6499
  • i'll do this in a separate PR