Looking at the test case, its current flow is typing in the credentials and then clicking on the log-in button. This logic does not cover the case where the credentials are incorrect, because after clicking on the log-in button the test already ends. I
If you are trying to fail the test case when the credentials are wrong, then you would need to do something like this:
// Type in username
// Type in password
// Click on log-in button
WebUI.verifyElementNotPresent(findTestObject('this is an object that appears ONLY when the credentials are incorrect'))
Then the test case would fail if the element which indicates the credentials appears on the page.
For example, on Github, if you type in the incorrect credentials then there is an error message on the web page.