The finale to the series ends without revealing whether or not Chris passed the GED. While it plays homage to The Sopranos, at the same time, it's a clever way of showing that Chris did in fact pass it. At the end of each episode, the punchline would involve Chris either failing at what he had attempted to do or otherwise the butt of the closing joke. In this case, it finally breaks the running gag by ending the show before revealing what happens.
In fact, since it's not just the episode that ends, but the entire series, we can assume that Chris passing the GED led to him starting his stand-up career, and thus he finally became the successful Chris Rock known today.