Question

I’m trying to test an ansynchronous callback by checking that it’s called, say, n times in m seconds.

Here’s my code so far:

test("async callback", function() {
    expect(1);
    var called = 0;

    var callback = function() {called++;};

    var model = new Model(callback);
    model.startCallbacks();

    function theTest() {         // call this a few seconds later and verify
        model.stopCallbacks();   //   that the callback has been called n times
        equal(3, called, "number of times callback was called");
    }

    setTimeout(theTest, 10000); // wait about 10 seconds until calling theTest
});

(model.startCallbacks and model.stopCallbacks are implemented with setInterval.)

This doesn’t work. I think it’s because execution goes off the end of the test function while callback is still being asynchronously executed.

What I want to test: that model is correctly calling callback. How do I do this?

Answer 1

// use asyncTest instead of test
asyncTest("async callback", function() {
    expect(1);
    var called = 0;

    var callback = function() {called++;};

    var model = new Model(callback);
    model.startCallbacks();

    function theTest() {         // call this a few seconds later and verify
        model.stopCallbacks();   // that the callback has been called
        equal(3, called, "number of times callback was called");

        // THIS IS KEY: it "restarts" the test runner, saying
        // "OK I'm done waiting on async stuff, continue running tests"
        start();
    }

    setTimeout(theTest, 10000); // wait about 10 seconds until calling theTest
});