The Duolingo English Test is scientifically designed to provide an accurate assessment of real-world language ability. The test adapts to each person's ability so that no two tests are alike. This prevents inflated scores achieved through memorization of test questions, a well-known problem in language certification
There are six grade levels, from Beginner to Expert. You can check them all out here, and you'll also be able to see examples of each level's strengths.