CODEWITHSUNDEEP
node.js
siyang
siyang

Reputation: 675

unit test the function with callback passed to another function

I'm not sure what is the best way to do unit test for function foo, since the callback is passed to function bar, the unit test for foo I wrote is also testing the function bar.

Is there any way I could only test the logic inside the foo? In below use case, I just want to make sure foo function can increase value by 1 then pass everything to bar. How bar handle the value should be tested in bar unit test not foo unit test.

function bar(value, callback) {
    value = value + 1;
    callback(value);
}

function foo(value, callback) {
    value = value + 1;
    bar(value, callback);
}


//test for function bar
it('should be able to increase value by 1', function (done) {
    bar(1, function (value) {
    expect(value).to.equal(2);
    done();
  });
});

//test for function foo
it('should be able to increase value by 2', function (done) {
    foo(1, function (value) {
    expect(value).to.equal(3);
    done();
   });
});

Upvotes: 0

Views: 768

Answers (1)

Aaron Dufour
Aaron Dufour

Reputation: 17505

This code is more or less analogous to the following synchronous code:

function bar(value) {
    value = value + 1;
    return value;
}

function foo(value) {
    value = value + 1;
    return bar(value);
}

Now that we're looking at something a little more familiar, we can ask your question again. The answer, clearly, is no - foo always calls bar.

If you can test both foo and bar, it shouldn't matter - based on which of those fail, you can figure out where the error is.

If bar is something like a db call, which you might not be able to test, you should look into the idea of "mocking" functions/objects. If bar isn't something that should be mocked, but foo should be tested without using bar, then this indicates that bar should probably be passed as an argument to foo, rather than hardcoded in to that function.

Upvotes: 1

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