Use cases and test cases are created to evaluate whether programs function as intended. At this level, students develop use cases and test cases with teacher guidance. Testing should become a deliberate process that is more iterative, systematic, and proactive than at lower levels. For example, students test programs by considering potential errors, such as what will happen if a user enters invalid input (e.g., negative numbers and 0 instead of positive numbers). Alternatively, in an interactive program, students could test that the character cannot move off of the screen in any direction, cannot move through walls, and can interact with other characters. They then adjust character behavior as needed.