Angular unit testing Filter Predicate function with Jasmine

Question

I have a filter predicate function which I use to filter a mat-table in angular

this.dataSource.filterPredicate = this.myService.tableFilter();

tableFilter(): (data: any, filter: string) => boolean {
    let filterFunction = function (data, filter): boolean {
      let filterValues = JSON.parse(filter);
      ... my logic ...
    };
    return filterFunction;
  }
}

I want to write a unit test to test this filter predicate function

it('filter table', inject(
    [MyService],
    (service: MyService) => {

      // how to do this?
      let messageObject = service.tableFilter(dummyData, 
        getDummyFilterValues());
    }
  ));

How do I call the service.tableFilter function in the unit test?

Answer 1

Replace the logic where I am returning an object in the below code with a boolean return in your case. I think the question is regarding how to call the returned function

typescript code

tableFilter(): (data: any, filter: string) => any {
    const filterFunction = (data, filter) => {
      const filterValues = JSON.parse(filter);
      return data.find(d => {
        return d.num === filterValues.num;
      });
    };
    return filterFunction;
  }

spec file/ unit test block

  it('test filterfx', () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    const filterfx =  app.tableFilter();
    expect(filterfx(app.data,  JSON.stringify({ num: 'one' })).num).toEqual('one');
  });