How to test promise with try and catch a function like this example-CodePudding

I cannot test the reject for some reason. Here is the function and I want to test it 100%. now it is like 92% and complain about reject(e) is not tested..

  public resolve(): Promise<{ [key: string]: boolean }> {
    return new Promise<{ [key: string]: boolean }>(async (resolve, reject) => {
      try {
        for await (const setting of settings) {
          // ObjectStore that acts like hashMap
          this.store.set(setting.key, setting.value);
        }
        resolve();
      }
      catch (e) {
        reject(e);
      }
    });
  }

Updates:

I have to make another Mock to make the catch statement happening first. And TestBed.overrideProvider is not really working for me, so that I have to

  it('should return a rejected promise', async() => {
    TestBed.resetTestingModule();
    TestBed.configureTestingModule({ 
//inserting the new mock provider to trigger the catch 
... 
});

and then use the answer below (Thank you @Apoorva Chikara) and works for me

If there is easier way to accomplish this, please let me know

CodePudding user response：

You can catch the error and test it. It is similar to testing the resolving.

  describe('Test Case', () => {
    describe('Testing Sample 1', () => {
      it('should return a rejected promise', () => {
        service.resolve()
          .catch((error) => {
            expect(error).toEqual('the error string');
          });
      });
    });
  });

CodePudding user response：

Never pass an async function as the executor to new Promise! Your function should be simplified to

public async resolve(): Promise<{ [key: string]: boolean }> {
//     ^^^^^
  for await (const setting of settings) {
    // ObjectStore that acts like hashMap
    this.store.set(setting.key, setting.value);
  }
}

and then you won't need a separate test for the code path that doesn't even exist. Furthermore, you probably don't want to use for await, unless settings is an asynchronous generator.