testing

Testing

Analyze code and generate meaningful tests. Not just "test the function" — understand what the code does, identify edge cases, and create tests that catch real bugs.

Rules

1. Read before testing — understand the code's purpose and dependencies before writing tests
2. AAA pattern — every test: Arrange (setup), Act (execute), Assert (verify)
3. One assertion per concept — test one behavior per it/test block
4. Test behavior, not implementation — test what the function does, not how it does it
5. Edge cases matter — null, empty, boundary values, error paths
6. Name tests descriptively — "should return 0 when cart is empty", not "test1"
7. No test interdependence — each test must work independently and in any order
8. Run after writing — always execute the tests to confirm they pass

Workflow

Phase 1: Analyze the code

1. Read the source file(s) to test
2. Identify:
   • Public API surface — exported functions, class methods, endpoints
   • Dependencies — what it imports, what needs mocking
   • Side effects — DB calls, HTTP requests, file I/O, timers
   • Edge cases — null inputs, empty arrays, boundary values, error conditions
   • Business rules — domain-specific logic that MUST be correct

Phase 2: Decide test type

What you're testing	Test type	Approach
Pure function (no side effects)	Unit test	Direct call, no mocks needed
Function with dependencies	Unit test	Mock dependencies, test logic in isolation
Multiple modules working together	Integration test	Minimal mocking, test the interaction
API endpoint	Integration test	Test request/response cycle
User workflow	E2E test	Test full flow from user perspective
Data transformation	Unit test	Input → expected output tables

Phase 3: Generate tests

Structure

describe('[ModuleName]', () => {
  describe('[functionName]', () => {
    // Happy path
    it('should [expected behavior] when [condition]', () => {
      // Arrange
      // Act
      // Assert
    });

    // Edge cases
    it('should [behavior] when input is null/empty/zero', () => { ... });
    it('should [behavior] when input is at boundary', () => { ... });

    // Error cases
    it('should throw/return error when [invalid condition]', () => { ... });
  });
});