ast-grep rule for when you're missing a `done` callback in an observable's `subscribe`. Only triggers when there are assertions inside the subscribe as we don't want to be too hasty.

missing-done-callback-in-subscribe.yml

  language: TypeScript
  id: missing-done-callback-in-subscribe
  message: When subscribing to an observable inside a test function, you must call the 'done' function. Otherwise the assertions will never run.
  severity: error
  note: | 
    When testing observables in Jest, you must call the `done()` function in the subscribe callback. Jest provides a `done` function to test functions that must be executed to let Jest know when the test is done.
    If you don't call the done function, the assertions will never run because Jest will finish the test before the subscribe callback is called.

    If possible, it is encouraged to use `firstValueFrom` or `lastValueFrom` instead of subscribing to an observable directly in a test function. These handle subscribing / unsubscribing for you.

    Incorrect code:
    
    ```ts
    it('works', () => {
      observable.subscribe((someData) => {
        expect(someData).toBeTruthy() // Will not run because no done function is called!
      })
    })
    ```

    Correct code:

    ```ts
    it('works', (done) => {
      observable.subscribe((someData) => {
        expect(someData).toBeTruthy()
        done() // Calling done after finished makes sure Jest waits for the assertions to run.
      })
    })
    ```
  rule:
    any:
      - matches: subscription
        inside:
          pattern: '$_.subscribe($$$_)'
          all:
            - pattern: $SUBSCRIPTION
          stopBy: end
          inside:
            pattern: 'it($$$_)'
            stopBy: end
            has:
              kind: arguments
              has:
                nthChild: 2
                any:
                  - pattern: 'function()  { $$$_ }'
                  - pattern: '() => { $$$_ }'
      - matches: subscription
        not:
          has:
            pattern: $DONE_FUNC()
            stopBy: end
        inside:
          pattern: '$_.subscribe($$$_)'
          all:
            - pattern: $SUBSCRIPTION
          stopBy: end
          inside:
            pattern: 'it($$$_)'
            stopBy: end
            has:
              kind: arguments
              has:
                nthChild: 2
                any:
                  - pattern: 'function($DONE_FUNC) { $$$_ }'
                  - pattern: ($DONE_FUNC) => { $$$_ }
                  - pattern: $DONE_FUNC => { $$$_ }
  labels:
    DONE_FUNC:
      message: The done callback is passed but is never called.
      style: primary
    SUBSCRIPTION:
      message: This subscription is missing a done callback.
      style: primary
    ASSERTION:
      message: This assertion will never run because there is no done callback.
      style: secondary
  files:
    - '**/*.spec.ts'
    - '**/*.test.ts'
  utils:
    subscription:
      any:
        - kind: arrow_function
        - kind: function_expression
      has:
        pattern: 'expect($$$_)'
        all:
          - pattern: $ASSERTION
        field: body
        stopBy: end