Create a new file `src/reverse.js` that exports a function `reverse(s)` which returns the input string with its characters in reverse order. Handle edge cases such as empty strings and non-string inputs (throw a TypeError). Add a corresponding test file `tests/reverse.test.js` using your project's testing framework. Write at least three test cases: 1. Normal string input (e.g., "world" → "dlrow"). 2. Empty string input (should return an empty string). 3. Non-string input (e.g., null) should throw a TypeError. Make sure the test imports the function correctly and all tests pass. No other code changes are required.