testing a typescript decorator

Question

I have a simple decorator to trigger either stopPropagation() or preventDefault() when certain conditions are met. I've tested this in my app and I'm sure the decorator is working properly. However I couldn't test the decorator, whether the aforementioned methods are triggered.

When executing the test I get this error:

 Error: Expected spy stopPropagation to have been called.

core.decorators.ts

export function eventModifier( stopPropagation = false, preventDefault?: boolean ) {
  return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    const originalMethod = descriptor.value;
    descriptor.value = function() {
      const context = this;
      const mouseEvent: MouseEvent = Array.from( arguments ).find( event => event instanceof MouseEvent );

      if ( stopPropagation ) {
        mouseEvent.stopPropagation();
      }

      if ( preventDefault ) {
        mouseEvent.preventDefault();
      }

      originalMethod.apply( context, arguments );
    };

    return descriptor;
  };
}

core.decorators.spec.ts

import { eventModifier } from './core.decorators';

describe('eventModifier decorator', () => {

  class TestClass {

    @eventModifier( true )
    public click( event: MouseEvent ): void {
    }

  }

  it('decorator is defined', function() {
    expect( eventModifier ).toBeDefined();
  });

  it('stopPropagation() should be called', function() {
    const testClass = new TestClass();
    const ev = new MouseEvent('click')

    spyOn( testClass, 'click' );
    spyOn( ev, 'stopPropagation' );

    testClass.click( <MouseEvent> ev );

    expect( testClass.click ).toHaveBeenCalledWith( ev );
    expect( ev.stopPropagation ).toHaveBeenCalled();
  });

});

Answer 1

After couple of days of fail and trial I figured it our. It appears that I forgot something while setting spy on testClass.click method.

Here is the working unit test:

 import { eventModifier } from './core.decorators';

describe('eventModifier decorator', () => {

  class TestClass {

    @eventModifier( true )
    public click( event: MouseEvent ): void {
    }

  }

  it('decorator is defined', function() {
    expect( eventModifier ).toBeDefined();
  });

  it('stopPropagation() should be called', function() {
    const testClass = new TestClass();
    const ev = new MouseEvent('click')

    spyOn( testClass, 'click' ).and.callThrough();
    spyOn( ev, 'stopPropagation' );

    testClass.click( <MouseEvent> ev );

    expect( testClass.click ).toHaveBeenCalledWith( ev );
    expect( ev.stopPropagation ).toHaveBeenCalled();
  });

});