Since this program is composed of a language interpreter and a game engine that are modular and complex in and of themselves, unit testing can be very useful in proving testing compliance. Since the unit testing system uses an extensive list of code snippets to test the system, it can be very useful to extensively test these things which are otherwise hard to test. Along with this the specification for the engine and language can be given to the client so that they have some context for the unit tests.
For the other aspects of Green Engine, such as the integration of all the components or to demonstrate the capabilities of the system relative to the language there will be a series of games written which will demonstrate the capabilities of the system and the language. These can also evolve to be game templates for the end product. For each version they will be as follows:
The last aspect of the testing would be a demonstration of the operational use cases. Since the user will be students this will be important so these should be done live to the client so that they can get a live feel instead of just a specification.
The primary feedback will come from the live demonstrations so that immediate and interactive feedback can be received. Other aspects such as the language specifications and the engine specifications can be analyzed in depth to give detailed feedback. The games themselves can also be taken away for feedback. As the project progresses and become more featureful and easier to use, feedback will become easier to come by.