FlexUnit4 user interface

That is what the assert classes do.

In the most basic sense, you have things like

assertEquals( 8, x );

Wherein, 8 is the expected value, and x is the real value. If it fails, the user interface will tell you to expected versus actual. More on this here:

http://docs.flexunit.org/index.php?title=Writing_a_Basic_Test

In the more complicated approach, you have Hamcrest assertions, which provide even more human readable failures. You can read more about these here:

http://docs.flexunit.org/index.php?title=Hamcrest

Mike