Testing Instructions

Testing Instructions

Test-First Discipline

Always write the failing test before the implementation.

The commit order is:

1. test(scope): failing test for [what you're building] — RED
2. feat(scope): implement [what you're building] — GREEN
3. refactor(scope): clean up [if needed] — REFACTOR

Never commit a test that already passes before you write the implementation.

Test Categories and Where They Live

Category	Location	What Goes Here
Unit	tests/unit/	Pure functions in src/utils/
Service	tests/integration/	Service functions with Firebase emulator
Component	tests/unit/	React component rendering and interactions
E2E	tests/e2e/	BDD scenarios (Cucumber + Playwright)

Unit Test Pattern

[PLACEHOLDER — replace with your actual test framework and patterns. Example using Jest:]

// tests/unit/utils/compoundInterest.test.ts
import { projectGrowth } from "../../../src/utils/compoundInterest";

describe("projectGrowth", () => {
  it("returns initial amount when rate is 0", () => {
    expect(projectGrowth(1000, 0, 12)).toBe(1000);
  });

  it("throws ValidationError for negative principal", () => {
    expect(() => projectGrowth(-100, 5, 12)).toThrow(ValidationError);
  });

  it("handles monthly compounding correctly", () => {
    // 1000 at 12% annual = 1126.83 after 12 months
    expect(projectGrowth(1000, 12, 12)).toBeCloseTo(1126.83, 1);
  });
});

What Every Test Must Have

• A describe block named after the function/component being tested
• At least one happy path test
• At least one error/edge case test (invalid input, empty state, network failure)
• Descriptive it() names — read like sentences: "returns X when Y"

What Tests Must NEVER Do

• Call live Firebase (use emulator or mock)
• Have side effects on other tests (clean up state in afterEach)
• Import from screens/ or components/ in unit tests for utils/
• Be deleted to make CI pass — fix the code instead