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I asked, "How to unit test a RxJS BehaviourSubject" and this was its answer is spot on, in my opinion, 😳! (check the answer below as a bonus 🥳)
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How to unit test an RxJS BehaviourSubject
Answer by ChatGPT
To unit test an RxJS BehaviorSubject
, you can subscribe to the subject and use the next
, error
, and complete
methods to push values and events into the observable stream and then use the toBe
or toEqual
matches provided by your unit testing framework to check the resulting values emitted by the subject.
Here is an example of how you might test a BehaviorSubject
using the Jasmine testing framework:
describe('BehaviorSubject', () => {
let subject: BehaviorSubject<number>;
beforeEach(() => {
// Create a new subject before each test
subject = new BehaviorSubject(0);
});
it('should emit the initial value to new subscribers', () => {
subject.subscribe(value => {
// Assert that the value emitted is the expected initial value
expect(value).toBe(0);
});
});
it('should emit the latest value to new subscribers', () => {
// Push a new value into the subject
subject.next(1);
subject.subscribe(value => {
// Assert that the value emitted is the expected latest value
expect(value).toBe(1);
});
});
});
In this example, the beforeEach
the function is used to create a new BehaviorSubject
with an initial value of 0
before each test. The first test case subscribes to the subject and asserts that the initial value is emitted when the subscription is created. The second test case pushes a new value into the subject using the next
method and then subscribes to the subject, asserting that the latest value is emitted to the new subscriber.