I have a doubt on Flex unit. Unit test cases are really required for flex application for displaying data.
So, you should remember that not everything in Flex is a UI Component.
I, personally, find that FlexUnit (or a unit testing framework) is great for testing services and other non-visual ActionScript / Flex classes. Was the property set after I set it? Was the order this ArrayCollection changed after I changed the value of the "orderBy" property on this custom class? Was my file created after I called a method to create the file?
These are things that unit testing can help answer.
With much of Flex, I find that UI testing, such as FlexMonkey or RIATest is much more applicable. Did this effect run after I change properties on the ViewStack? Did the background color change after I clicked this button? Was the second ComboBox populated with dat after I selected a value in the first Combobo?
these are the sort of questions that User Interface testing can help with.