Karma-Jasmine for.sort() 中的单元测试故障排除 Angular 中的 function

Question

I have a block of code written in Angular:

this.selectedData.sort((a, b) => {
        if (query === 'poll' && (a[query] === null || b[query] === null)) {
          return a[query] === null ? 1 : -1;
        } else if (query === 'submit') {
          return moment(a[query]).isBefore(moment(b[query])) ? 1 : -1;
        } else {
          return b[query].localeCompare(a[query]);
        }
});

I tried writing a callFake for the sort function like below:

spyOn(selectedData, 'sort').and.callFake((a, b) => {
     expect(query).toBe('poll');
});

But, the code-coverage shows, it is not going inside the sort function block. Is there any other way of writing the test cases. I also tried using callThrough() and it is showing me the same result.

Answer 1

spyOn installs a spy onto an existing object but it does not invoke the specified method. By chaining the spy with and.callFake , all calls to the spy will delegate to the supplied function instead of the object's method. What you need is...

// Install spy (without delegating)     
spyOn(selectedData, 'sort');

// Invoke the object's method
const result = selectedData.sort(...);

// Compare actual result with expected result
expect(result).toBe(<expectedResult>);