Implement ruleTestRunner as mocha tests.

[NaridaL]

A couple of reasons:

• Outputting a diff on errors is non-trivial and should be handled externally, the current implementation breaks in some cases. Mocha handles this.

mocha output:

current impl. output:

• Better integration with existing environments. E.g. WebStorm shows a nice tree view of test runs and allows failed tests to be viewed in an external diff viewer.

• Currently running a single test requires using the CLI --test param, which isn't intuitive.

I'm willing to implement the change.

[giladgray]

@NaridaL i'm not convinced we need to bring in mocha to solve this problem (vs simply a better diff solution). we use babel-code-frame for the diffing but maybe we can use it better?

[NaridaL]

Yeah just for the first point it's probably unnecessary. But being able to click "view diff" in WebStorm is amazing :-D

[JoshuaKGoldberg]

💀 It's time! 💀

TSLint is being deprecated and no longer accepting pull requests for major new changes or features. See #4534. 😱

If you'd like to see this change implemented, you have two choices:

• Recommended: Check if this is available in ESLint + typescript-eslint ✅
• Not Recommended: Fork TSLint locally 🤷‍♂️

👋 It was a pleasure open sourcing with you!

If you believe this message was posted here in error, please comment so we can re-open the issue!

[JoshuaKGoldberg]

🤖 Beep boop! 👉 TSLint is deprecated 👈 (#4534) and you should switch to typescript-eslint! 🤖

🔒 This issue is being locked to prevent further unnecessary discussions. Thank you! 👋