The current state of the support of Unit Tests and Run Configurations is the following:

On my local built, I have successfully created a version that supports Run Configurations. It is possible to start Mathematica from IDEA and through parameters it will be further possible to load a package at startup and open files etc.

A more sophisticated support of communication between IDEA and Mathematica requires to maintain a MathLink connection and to control the front end completely over this connection (it is exactly what is done in Workbench). This would be a lot of work (I guess about 5k lines of code) and more important, it won't be possible easily because controlling the front end with FronEndTokens is not documented well.

Nevertheless, I'm having good hope that a support of MUnit is still possible by simply running the test-files as commandline parameter and interpreting the result in IDEA. This shouldn't be too much work, but currently I'm having no hope of finding the time to work on it.

The reason for this is that the stack of work that needs to be done is constantly growing since a few months and I need to deal with a strange situation right now.

I guess I don't want to go into more detail on a public forum.