New rule request: no-hooks

[macklinu]

eslint-plugin-mocha has a rule called no-hooks that I think could be a good addition to this ESLint plugin. I think the mocha/no-hooks docs as well as this tweet help explain how using nested describe() and beforeEach() hook functions can result in harder to follow code / shared state between tests.

I think when combined with jest/consistent-test-it, you could enforce tests that look more like:

function setupFoo(options) { /* ... */ }
function setupBar(options) { /* ... */ }
function setupBaz(options) { /* ... */ }

test('foo does this', () => {
  const foo = setupFoo({ /* options */ })
  expect(foo).toEqual(/* expected */)
})

test('bar does this', () => {
  const bar = setupBar({ /* options */ })
  expect(bar).toEqual(/* expected */)
})

test('baz does this', () => {
  const baz = setupBaz({ /* options */ })
  expect(baz).toEqual(/* expected */)
})

instead of looking like this:

let foo
let bar
let baz

beforeEach(() => {
  foo = setupFoo()
  bar = setupBar()
  baz = setupBaz()
})

afterEach(() => {
  foo = null
  bar = null
  baz = null
})

test('foo does this', () => {
  expect(foo).toEqual(/* expected */)
})

test('bar does this', () => {
  expect(bar).toEqual(/* expected */)
})

test('baz does this', () => {
  expect(baz).toEqual(/* expected */)
})

I think there are times when using setup and teardown hooks are necessary, but I find that they can often be avoided. I could see this rule providing an option that would whitelist allowed hook function names, or the user could disable with // eslint-disable-next-line jest/no-hooks.

Thoughts on this rule? Would you accept a PR for this feature?

[SimenB]

Yeah, this sounds like a reasonable rule! PR most welcome 🙂

[thymikee]

I think @thejameskyle will like it 😅
Re: https://twitter.com/thejameskyle/status/954906997169664000

[macklinu]

I will look to contribute a PR for this today. 🌴