angular service unit test DoneFn

Question

I'm following the angular official doc and I can see this code:

it("#getObservableValue should return value from observable", (done: DoneFn) => {
    service.getObservableValue().subscribe(value => {
      expect(value).toBe("observable value");
      done();
    });
  });

I'm wondering where DoneFn comes from because I've no error either import for the typing.

Answer 1

If you follow the Interface definition you will see that it is under:

node_modules/@types/jasmine/index.d.ts

/** Action method that should be called when the async work is complete */
interface DoneFn extends Function {
    (): void;

    /** fails the spec and indicates that it has completed. If the message is an Error, Error.message is used */
    fail: (message?: Error | string) => void;
}

You don't need to import or use it, it's mostly for reference. I am not sure how @types exactly work but I suppose if there is a @types typing within the project, node knows how to find the definition as they are all indexed in this one folder.

UPDATE:

I found out this is being configured by tsconfig.json

"typeRoots": [
  "node_modules/@types"
],