How to test Input and mat option inside Mat select in Angula

I have the following below code in my Html file :

 

Product.html

 

I want to write Unit test case in Angular for input element inside mat-select element in .ts file like below:

 

it('open the product dropDown', async(() => { componentFixture.detectChanges(); spyOn(searchComponent, 'filterProducts'); let input = componentFixture.debugElement.query(By.css('#txtFilterProduct')); input.triggerEventHandler('keyup', null); componentFixture.detectChanges(); expect(searchComponent.filterProducts).toHaveBeenCalled(); expect(searchComponent.filterProducts).toHaveBeenCalledTimes(1); }));

 

I am getting the error: calling triggerEventHandler on undefined. Similarly it is giving the same error for mat-option.

 

Please suggest or tell how we can do unit test for input and mat-option inside mat-select for dropdown