Support `max-describe-nesting-level` rule.

Currently we don’t have any rule that could control level of describe’s nesting.

rules: {
   "jest/max-describe-nesting-level": ["warn", {limit: 1}]
},

Good

describe('getSomething', function () {
    it('should get green plastic chair with `green` argument', () => {
      expect(getSomething('green').toBe('Green plastic chair'))
    });
});

Bad

describe('getSomething', function () {
    describe('w/o arguments', function () {
      it('should get orange jacket', () => {
        expect(getSomething().toBe('Orange jacket'))
      });
    })
});

I can implement this (with better examples 👀) if you are good with this rule?

[yavorsky]

@G-Rath Thanks for this!

I’ll work on your branch and can open a PR into it unless you merge it before.

Anyway this change shouldn’t affect a lot of files across project and just add new one, so rebasing wouldn’t be a problem here.

[G-Rath]

Go for it!

I’m actually literally right in the middle of making a big PR for the final round of TS conversations, which includes a new set of Typescript guards & whatnot, so I’d advise branching off that branch when doing the implementation.

I don’t expect that to have a big impact on your PR, and more than happy to help you rebase if needed - it’s just mainly that there’s a lot of JS -> TS renames, so it might make your fork & local git sad 😬

It’s going to be a busy week for me as I can finally do a lot of the small cleaning & refactoring that I’ve had to put off to land my PR 😂

Hopefully I’ve not scared you off - I’m actually excited for this rule, b/c it’ll hopefully mean breaking out the “find test case” logic used in a few of the rules into some nice & small utility functions 😄