I'm about to launch my app and I need unit tests covering the business logic that would hurt the most if it broke. First, scan my codebase and identify the functions that handle: payments and price calculations, authentication and session logic, authorization checks (who can access what), and any data transformations that write to the database. List what you find before writing anything so I can confirm the priorities. Then, for each critical function, write unit tests that cover: 1. The happy path with realistic input. 2. Empty, null, or undefined input. 3. Malformed input (wrong types, oversized values, unexpected shapes). 4. Boundary conditions (zero, negative numbers, maximum values). 5. Any branching logic where a wrong branch would charge the wrong amount, leak data, or grant access it shouldn't. Use the test framework already in my project. If there isn't one, tell me which one you'd recommend for my stack and wait for my confirmation before adding it. Don't mock the entire world. Only mock external services (payment providers, email, third-party APIs). Let the real logic run. Don't write tests that just assert the mock was called. When you're done, show me how to run the tests and confirm they all pass. If any test fails against the current code, stop and show me the failure before changing the implementation, because a failing test on launch eve might be a real bug.