QUnit and a fail JSONP scenario

Question

I want to test that my web app handles a failure scenario and displays the corresponding error message using QUnit.

My app performs a JSONP request to get its initialization contents. I want to test the case where my Data Source is unavailable upon startup. This scenario results in an error on the underlying JQuery code, which I believe QUnit is intercepting and capturing it as a failed assertion, even though that is the expected behavior.

My app code looks like this:

loadContents() {
    $.ajax({
        url: initURL,
        dataType: 'jsonp',
        timeout: timeout,
        success: initializeDisplay,
        error:   displayErrorMessage,
    });
}

My test case looks like this:

asyncTest("Invalid initialization host", 1, function() {
    initURL = invalidURL;
    loadPageContents();
    index = $("#error-message-div").text().indexOf(errorMessage);
    ok(index > -1, "Error message not found");
})

When I run my test, I get an extra assertion, which always fails. The assertion contains the message: "Error loading script" with a URL to the JSONP GET request.

The issue I believe I am running into is that since the JSONP callback is never executed, it throws an exception which QUnit believes to be a failed assertion.

Any ideas how I could get my test to execute without registering the exception as a failure?

Update - To clarify, the QUnit assertion works as expected, however I am somehow getting an additional assertion, which fails always.

Thanks!

Answer 1

Knowing that the cause was that the JSONP call was failing on the background, in order to suppress this error during testing I had to add an error handler to the document object when the error was expected.

  errorNamespace = "error.test"
  $(document).on(errorNamespace, function(event) {
      ok(true, "Received expected error");
      // Prevent the error from propagating into the assertion
      event.stopPropagation();
      // Remove the error handler to allow other errors to flow
      $(document).off(errorNamespace);
  });

Unfortunately, the error event does not contain any information that would help me verify that the caught error is the one I expected, which can be troublesome.