Hmm... could the name of this function be clarified, alternatively a comment added to the docstring, that states specifically that this is for testing build failure due to load balancer issues - e.g. the failures that trigger server deletion happens after a long time.

Otherwise if this were used to test, say, an invalid image the test might fail due to timing.  (e.g. by the time you check the state and assert that there are X desired servers in the group, that number may already have gone down to to build failure).