Creating a Mock ErrorHandler in Angular to Handle Rethrown throwErrors (using jasmine)

Question

Creating a Mock ErrorHandler in Angular to Handle Rethrown throwErrors (using jasmine)

When using Jasmine, I have implemented tests to handle error logic from a subscribed Observable.

    this.apiService
      .post({})
      .pipe(
        take(1),
        catchError((e) => {
          return throwError(() => e);
        })
      )
      .subscribe(() => {});

The goal is to rethrow the error so it can be managed outside of the component in a custom error handler.

Chrome Headless 109.0.5412.0 (Linux x86_64) ERROR
  An error was thrown in afterAll
  [object Object] thrown
  [object Object] thrown
  [object Object] thrown

I initially attempted to override the ErrorHandler with a spy, but it did not have any effect.

I also experimented with using the jasmine.spyOnGlobalErrorsAsync, which still resulted in errors being produced.

Any suggestions or ideas on how to address this issue?

angular typescript unit-testing rxjs jasmine

Answer 1

Answer №1

To handle nested unhandled exceptions within observables, consider using fakeAsync along with flush or tick inside a try-catch block.

it("should trigger uncaught exception in case of service error", fakeAsync(() =>
{
  // Arrange
  apiServiceSpy.post.and.returnValue(throwError(() => new Error("Failed service call")));

  // Act
  component.methodThatSubscribesToApiServicePost();
  let error: unknown = undefined;
  try
  {
      flush();
  }
  catch (ex)
  {
      error = ex;
  }

  // Assert
  expect(error?.message).toBe("Failed service call");
}));

If you have a custom global ErrorHandler (e.g. CustomErrorHandler implementing ErrorHandler), it should be tested separately.

Answer 2

To handle nested unhandled exceptions within observables, consider using fakeAsync along with flush or tick inside a try-catch block.

it("should trigger uncaught exception in case of service error", fakeAsync(() =>
{
  // Arrange
  apiServiceSpy.post.and.returnValue(throwError(() => new Error("Failed service call")));

  // Act
  component.methodThatSubscribesToApiServicePost();
  let error: unknown = undefined;
  try
  {
      flush();
  }
  catch (ex)
  {
      error = ex;
  }

  // Assert
  expect(error?.message).toBe("Failed service call");
}));

If you have a custom global ErrorHandler (e.g. CustomErrorHandler implementing ErrorHandler), it should be tested separately.

Creating a Mock ErrorHandler in Angular to Handle Rethrown throwErrors (using jasmine)

Answer №1

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