It is often useful to wait for a condition before performing an assertion.

"waitForCondition" is a feature that can greatly accelerate asynchronous tests.

With `waitForCondition`, when the condition is met, the test can continue. With `wait`, OTOH, the test must wait the entire duration. The difference with waitForCondition, is that, unlike `wait` the
deferred segment can run as soon as the condition is met. This results in the test finishing much more quickly. When several tests functions are refactored to use waitForCondition over wait, the time
saved for each test is compounded and the time the test case takes to complete can be reduced by several seconds.

(Copied from: http://yuilibrary.com/projects/yui2/ticket/2528872)