testing-debugging

Testing and Debugging

This skill guides debugging deployed applications and writing tests for rapid iteration. The key insight: unit tests are the fastest way to reproduce and fix bugs.

The Unit Test Debugging Workflow

This is the most effective debugging workflow. Instead of repeatedly deploying and manually testing in the browser, write a unit test that reproduces the bug:

Why Unit Tests for Debugging?

Approach	Cycle Time	Reliability
Deploy → Browser → Manual test	30-60 seconds	Variable
Run unit test	1-2 seconds	Consistent

A 30x speedup means you can iterate 30 times faster. This compounds: what takes an hour with manual testing takes 2 minutes with unit tests.

The Workflow

1. Understand the bug - Read the user report, check console errors, understand expected vs actual behavior

2. Write a failing test - Create a test that reproduces the exact failure

   // Example: User reports "discount not applied to cart total"
   test('applies discount code to cart total', () => {
     const cart = createCart([
       { name: 'Widget', price: 100 },
       { name: 'Gadget', price: 50 }
     ]);
   
     cart.applyDiscount('SAVE20'); // 20% off
   
     expect(cart.total).toBe(120); // Was returning 150
   });
   

3. Run the test to confirm it fails - Verify you've reproduced the bug

   bun test
   

4. Fix the code - Make changes to fix the failing test

5. Run the test again - Confirm the fix works

   bun test
   

6. Deploy - Once tests pass, publish through the mediated project tool (not a package-manager or Wrangler deploy command)

   await tools.deploy_project({ project: "<project-name>" });
   

Test File Location

Place test files next to the code they test:

src/
  cart.ts
  cart.test.ts      # Tests for cart.ts
  utils/
    discount.ts
    discount.test.ts

Or use a __tests__ directory: