Encountering an error while unit testing Angular components with MatDialog: "Error: <spyOn>: open has already been spied upon."

Once I create an HTML file with a button, I trigger a poll to appear after an onClick event. Then, when the "submit" button is clicked on the dialog window, it closes and I intend to execute subsequent methods.

In my TypeScript file:

openDialogWindow() {
const dialogRef = this.dialogWindow.open(PollComponent, {
  width: '400px',
  height: '400px',
  data: getData()
});

dialogRef.afterClosed().subscribe(result => {
  if (result.status == 'VALID') {
    answerForm = result;
    this.callNextFunction();
  }
});

}

Afterwards, I proceeded to create a unit test in the spec.ts file:

it('should call dialog window and invoke methods after submission', () => {
service.callNextFunction.and.returnValue(of({value: 0}));

const result = new FormGroup({}, )
result.setValidators(null);
spyOn(component.dialogWindow, 'open')
  .and
  .returnValue({
    afterClosed: () => of(true)
  } as MatDialogRef<typeof component>);
  
fixture.detectChanges();
expect(component.dialogWindow.afterAllClosed).toContain(result);
expect(service.callNextFunction).toHaveBeenCalled();
expect(component.otherForm.recommendedValue.control.value).toEqual('123');

});

However, during testing, I encountered an error:

Error: <spyOn> : open has already been spied upon
Usage: spyOn(<object>, <methodName>)

Could this be due to the creation of:

matDialogSpy = createSpyObj<MatDialog>('MatDialog', ['open']);

within the beforeEach block? I utilize matDialogSpy in another unit test to verify if the dialog window opens upon clicking the button:

it('should open dialog when button has been clicked', fakeAsync(() => {
clickOnSlsButtonByLabel('Open dialog', fixture);

expect(matDialogSpy.open).toHaveBeenCalledTimes(1);
expect(matDialogSpy.open).toHaveBeenCalledWith(
  PollComponent,
  {
    width: '400px',
    height: '400px',
    data: data...
  }
);

}));

Answer №1

Remember, an exception is pretty clear - it's essentially a spy itself, so just make use of it

Keep in mind to swap out component.dialogWindow with whatever you have set up as your MatDialog in the test

component.dialogWindow.open //maybe matDialogSpy.open??
  .and
  .returnValue({
    afterClosed: () => of(true)
  } as MatDialogRef<typeof component>);

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