Are you ready to put Jest to the test by checking the completion event of

Question

Are you ready to put Jest to the test by checking the completion event of

The RxJS library's Observer triggers three main events:

complete
error
next

If we want to verify the occurrence of the complete event using Jest, how can this be achieved?

For instance, we are able to test the next and error events by checking for data passed within those functions:

o.subscribe(result => {
  expect(result.data.length).toEqual(1);
}, 
(e)=>{expect(e).toBeFalsy()}, 
()=>{ WHAT TO EXPECT HERE? }

Unlike the other events, the complete event does not pass any data. Its function signature is ()=>void. How can we verify this specific function signature?

Furthermore, regarding the line (e)=>{expect(e).toBeFalsy()}, since it doesn't actually trigger, is there a way to confirm that a certain callback is not executed?

javascript typescript rxjs jestjs

Answer 1

Answer №1

const convertToPromise = obs =>
  new Promise((resolve, reject) => {
    obs.subscribe({ complete: resolve, error: reject });
  });

import { fetchUserEvents } as user from '../user';

// Ensure that a promise is returned.
it('handles promises correctly', () =>
  expect(convertToPromise(fetchUserEvents(4))).resolves.toEqual('Mark'))

Source:

Additionally, Jest will trigger a failure if any Errors are thrown, allowing for use of various testing frameworks within its tests. For example, import 'rxjs/testing', as explained here

Answer 2

const convertToPromise = obs =>
  new Promise((resolve, reject) => {
    obs.subscribe({ complete: resolve, error: reject });
  });

import { fetchUserEvents } as user from '../user';

// Ensure that a promise is returned.
it('handles promises correctly', () =>
  expect(convertToPromise(fetchUserEvents(4))).resolves.toEqual('Mark'))

Source:

Additionally, Jest will trigger a failure if any Errors are thrown, allowing for use of various testing frameworks within its tests. For example, import 'rxjs/testing', as explained here

Answer 3

Answer №2

Discover how to verify that the error callback is not triggered here.

Seems like this piece of code will check the complete callback:

let complete = false;
let completeHandler = ()=>{
  complete = true;
  expect(complete).toBeTruthy()
};
let errorHandler = (e)=>{
  console.log("THIS IS NEVER EXECUTED");
  console.log("HOW DO WE VERIFY THAT IT IS NOT?");
let o:Observable<Result> = fn(data, errorHandler, completeHandler);
o.subscribe();

The errorHandler and completeHandler are integrated into the Observable<Result generated by the fn function.

Answer 4

Discover how to verify that the error callback is not triggered here.

Seems like this piece of code will check the complete callback:

let complete = false;
let completeHandler = ()=>{
  complete = true;
  expect(complete).toBeTruthy()
};
let errorHandler = (e)=>{
  console.log("THIS IS NEVER EXECUTED");
  console.log("HOW DO WE VERIFY THAT IT IS NOT?");
let o:Observable<Result> = fn(data, errorHandler, completeHandler);
o.subscribe();

The errorHandler and completeHandler are integrated into the Observable<Result generated by the fn function.

Are you ready to put Jest to the test by checking the completion event of

Answer №1

Answer №2

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