Fail tests if error is logged

[matthew-white]

Right now, tests as a whole fail if anything logs a warning. We've seen cases where a test manages to pass despite Vue logging a warning about something important that needs to be addressed, which is why this check is in place. This issue is to make it so that tests fail if anything logs an error as well.

One place this comes up specifically is with mockHttp(). If a test sends a request without using mockHttp(), that will log an error. However, at the moment, that doesn't lead to tests actually failing. It's easy to miss this error being logged.