Create a new file `src/capitalize.js` that exports a function `capitalize(s)` which returns the input string with the first character converted to uppercase and the rest unchanged. Handle edge cases such as empty strings and non-string inputs (throw a TypeError). Add a corresponding test file `tests/capitalize.test.js` using your project's testing framework (e.g., Jest, Mocha). Write at least three test cases: 1. Normal string input (e.g., "hello" → "Hello"). 2. Empty string input (should return an empty string). 3. Non-string input (e.g., 123) should throw a TypeError. Ensure the test imports the function correctly and all tests pass. No other code changes are required.