Test cases play a crucial role in competitive programming because they allow you to verify that your solution works as expected for all inputs, including edge cases. When you solve a problem, it's important to test your code on both sample test cases provided by the platform and on additional cases that you come up with. Sample test cases usually cover basic scenarios, but they might not be comprehensive enough to catch all possible bugs or edge cases. Creating your own test cases is key to ensuring that your solution handles extreme inputs or unexpected situations. For example, if the problem allows input arrays of size up to 100,000, you should test your code with an array of exactly that size to ensure it runs efficiently within the time limit. Similarly, if the problem involves strings, test with strings of different lengths, empty strings, or strings with repeated characters. When writing test cases, try to think of the most unusual or tricky inputs that could potentially break your code. Running your code on a variety of test cases helps you catch logical errors, such as off-by-one errors, incorrect variable initialization, or faulty loop conditions. It also helps you identify inefficiencies, such as slow algorithms that fail to run within the time limit for large inputs. By thoroughly testing your code, you increase your chances of submitting a correct and efficient solution during a competition.