• Create a test suite class
• Create a test case class
• Create a test case class of an exist class and choose which methods to test.
• Right click a test case class and run it.
• Right click a test suite class and run it.
• Choose any set of test suites and test cases (test methods) to run.
• See test results in FlexUnit Results View

To see more detail Click Here.

They are good for unit test, but not for TDD (write test before code).
I wish to see some more:

• Set the source folder for real code and tests folder for test classes.
• Create a test case class in the tests folder, and choose if create the class to be tested in the source folder.
• Create and update test suite classes automatically in every package in the tests folder.