Unexpected error during jasmine test (with observable) - rxjs

Question

I wrote a test for the following method:
private _segmentationStatus$: Subject<string> = new Subject();
public readonly segmentationStatus: Observable<string> = this._segmentationStatus$.asObservable();
/**
* Get the status from the segmentation service.
*/
public getStatus() {
const segmentationId: string = this._segmentationIdService.segmentationId;
const segmentationStatusUrl = `${this.getSegmentationStatusUrl}/${segmentationId}/status`;
this._http
.get(segmentationStatusUrl, { responseType: 'text' })
.subscribe({
next: () => {
this._loggerService.trackTrace(`Segmentation status: ${status}`, LogSeverity.Verbose);
this._segmentationStatus$.next(status);
},
error: (error) => {
this._messageService.emitMessage(new Message(MessageCode.ErrorGetStatus, error));
this._loggerService.trackException(error);
this._segmentationStatus$.error(error);
}
});
}
To test the method I started to write a test as below:
fit('should emit a message if the request failed', done => {
let messageReceived: Message;
spyOn((service as any)._messageService, 'emitMessage').and.callFake(message => {
messageReceived = message;
});
service.segmentationStatus.subscribe({
error: () => {
expect(messageReceived.messageCode).toBe(MessageCode.ErrorGetStatus);
done();
}
});
spyOnProperty(
(service as any)._segmentationIdService,
'segmentationId',
'get'
).and.returnValue('id');
service.getStatus();
httpTestingController
.expectOne(`${service.getSegmentationStatusUrl}/id/status`)
.flush('{}', { status: 500, statusText: 'status' });
});
If I use the debugger the flow of the program and test is as expected. I see the emitted message and the error handler in the unit test is called. However, after the error handler in the unit test completes the line this._segmentationStatus$.error(error); in the productive code throws another error, which is not handled. Thus the tests fails with the message Uncaught [object Object] thrown.
I`ve read the RxJS documentation and googled the problem, but was not able to figure out what I need to do pass the test. Any help to point out where I did the mistake would be highly appreciated.

Answer 1

I've found the problem; there was another subscriber to segmentationStatus which did not handle the error. As nobody "trapped" the exception it bubbled up and was re-thrown. As explained in On The Subject Of Subjects (in RxJS).