Memory leak is a bug that pretty hard to deal with. Usually people use some profilers to observer the memory usage while stressing the program, if there is no increase of memory usage after repeating calls of a function, we can conclude there is no memory leak in that function. It is of course fine to detect memory leak in this way, but it is always good to have a way that asserts your objects are really GC‘ed at some point.
The trick is to use a Dictionary with weak-reference keys and check its
element count. It is already quite popular in the Java world but look
like there aren’t many Flash devs talking about it.
A simple demo on how to write such test, source is available in wonderfl: