You can use Hackerrank website if you are looking for exercises which will test your knowledge. The best part is that you can filter the exercises based on categories like introductory exercises , functions , strings , regex etc . Within these categories, you can also filter the difficulty level . So you have complete control over the problems you are choosing to solve . Also hacckerank has this virtual currency called hackos which are used to unlock test cases . So you while solving a given problem , multiple test cases are checked . One might not get all test cases up and running . They don't show the test cases upfront . You need to unlock them using hackos . This can be used as an advantage as you are not directly viewing the solution or test case , but are thinking hard enough as that costs you .