Std Testing

Testing Standards

Rules for writing and maintaining tests. Quality tests are as important as quality code.

AAA Pattern

Structure every test with Arrange, Act, Assert, separated by blank lines:

it("should return user profile when valid ID is provided", async () => {
  // Arrange
  const userId = "user-123";
  const expectedUser = { id: userId, name: "Jane Doe", email: "jane@example.com" };
  mockUserRepo.findById.mockResolvedValue(expectedUser);

  // Act
  const result = await userService.getProfile(userId);

  // Assert
  expect(result).toEqual(expectedUser);
  expect(mockUserRepo.findById).toHaveBeenCalledWith(userId);
});

Test Naming

Pattern: should [expected behavior] when [condition]. describe blocks name the unit under test.

// Good
"should throw NotFoundError when user does not exist"
"should return paginated results when page parameter is provided"

// Bad
"test user"  "works correctly"  "error case"

describe("UserService", () => {
  describe("getProfile", () => {
    it("should return user profile when valid ID is provided", ...);
    it("should throw NotFoundError when user does not exist", ...);
  });
});

One Assertion Concept Per Test

• Each test verifies one logical concept, not one literal assertion.
• Multiple related assertions on the same result are fine (status code + response body).
• If a test needs a second "Arrange" for a second check, it is a second test.

Test Independence

• Every test must pass in isolation and in any order. No interdependency.
• No shared mutable state. beforeEach for setup, never beforeAll with mutation.
• Each test builds its own data — use factory functions/builders with overrides (buildUser({ role: "admin" }), create(:customer, :member)).

Mocking Strategy

• Mock external dependencies: databases, APIs, file systems, email services, third-party SDKs.
• Do not mock internal logic. If you must mock internal functions to test a unit, the design needs refactoring — inject the dependency instead.
• Prefer stubs and fakes over complex mock chains. Painful mocking is a design signal.
• Reset mocks between tests: beforeEach(() => vi.clearAllMocks()).

Coverage Targets

• Business logic: 80% minimum — services, domain models, validators, utilities.
• Overall project: 60% minimum — including infrastructure, config, glue code.
• Critical paths: 100% target — authentication, authorization, payments, data validation.
• Coverage is a floor, not a ceiling. Focus on branch coverage, not line coverage. High coverage with weak assertions is worse than moderate coverage with meaningful tests.

Test Types

• Unit: fast, isolated, no I/O. One module. The base of the pyramid — many of these.
• Integration: real DB / real router across modules. Some of these.
• E2E: complete user flows, critical paths only. Slow and brittle by nature — few of these.
• Contract: validate API contracts at service boundaries (Pact or similar).

Edge Cases

Every suite covers all five: null/undefined, empty (string/array/zero), boundary (min/max, pagination and length limits), error paths (network failure, invalid data, unauthorized, timeout), and concurrency where applicable.

Anti-Patterns to Avoid

• Testing implementation details — test behavior, not internal calls or private state.
• Snapshot overuse — snapshots hide intent and fail on cosmetic changes. Use sparingly.
• Flaky tests — fix or delete immediately. A flaky test is worse than no test.
• Commented-out tests — delete them; version control keeps history.
• Testing framework code — do not test that your ORM saves or your HTTP library sends requests.

Deep guides (read on demand, do not preload)

• Unit vs integration, mock boundaries, test data builders, edge-case matrix, Sidekiq jobs → references/test-strategy.md
• Vitest + RTL setup, query priority, userEvent, MSW, providers, Zustand, Framer Motion, ApexCharts → references/react-components.md
• Next.js Server Components, server actions, generateMetadata, route handlers → references/nextjs-server.md
• React Native: RNTL, navigation, Reanimated, MMKV, Centrifugo → references/react-native.md