The best form of test promotion for your casino is to conduct a review campaign that way, you have many who subscribe to that promotion to be able to be part of the casino after giving their honest reviews about you casino.
I agree that review campaign can bring a lot of good ideas on casino flaws or suggestion to improve the platform.
The task given to review manager will be assess quality of reviews and pay good reviews than bad, low quality reviews. But a good review does not have to write good words about the casino but should have many points on the casino flaws, game flaws that are meaningful for the team to improve the platform, security as well as their products.