The answer to this question depends on your goals and how much time you have available to study. If you want to increase your language skills so that you can function in the foreign world, then a proficiency test is an excellent way to do that. However, if you only want to improve your conversational ability in your target language, then focusing exclusively on learning grammar and vocabulary might be a better approach. Ultimately, it’s up to you to decide whether taking a proficiency test is the right step for you.