Test cases play a crucial role in competitive programming as they validate the correctness and robustness of a solution across a range of inputs. Creating comprehensive test cases ensures that the solution performs well under typical conditions, handles edge cases, and remains efficient even under worst-case scenarios. Edge cases might include inputs like zero, negative values, or extremely large inputs, depending on the problem requirements. Competitive programmers should also consider cases where the output might be unexpected, such as duplicate values or empty inputs. By designing and testing with diverse cases, programmers can catch potential errors or weaknesses in their approach. Testing iteratively during problem-solving enables prompt identification and rectification of bugs, leading to more reliable code. Moreover, practicing with challenging test cases helps improve debugging skills, instilling a habit of thorough testing before submitting solutions in competitions. Effective test case design is an essential skill that distinguishes consistent performers in competitive programming.