What does FlexUnitCompilerApplication.mxml do?
Flash Builder Premium users should be familiar with two .mxml files that are generated when they choose the "Run FlexUnit Tests" button as shown.
Flash Builder will auto generate FlexUnitApplication.mxml amd FlexUnitCompilerApplication.mxml.
There are several situations in which you will need to edit FlexUnitApplication.mxml, but this is not the case with FlexUnitCompilerApplication.mxml. This file is merely generated so that Flash Builder can ensure the tests, test cases, and test suites being run are linked into the SWF that is executing.