Compass/docs/TESTING.md

Testing

Why we test

Testing exists to give us fast, reliable feedback about real behavior so we can ship with confidence.

• Prevent regressions: Lock in correct behavior so future changes don’t silently break working features.
• Enable safe refactoring: A trustworthy suite lets us improve design without fear.
• Document intent: Tests act as living examples of how modules and components are expected to work.
• Catch edge cases early: Exercise unhappy paths, timeouts, and integration boundaries before production.
• Increase release confidence: Unit/integration tests plus a few critical E2E flows gate deployments.

What testing is not

• Not a replacement for monitoring, logging, or manual exploratory testing.
• Not a quest for 100% coverage—optimize for meaningful scenarios over raw numbers.

How we apply it here

• Unit and integration tests live in each package and run with Jest (see jest.config.js).
• Critical user journeys are covered by Playwright E2E tests under tests/e2e (see playwright.config.ts).

Test types at a glance

This project uses three complementary test types. Use the right level for the job:

• Unit tests

  • Purpose: Verify a single function/module in isolation; fast, deterministic.
  • Where: Each package under tests/unit (e.g., backend/api/tests/unit, web/tests/unit, common/tests/unit, etc.).
  • Runner: Jest (configured via root jest.config.js).
  • Naming: *.unit.test.ts (or .tsx for React in web).
  • When to use: Pure logic, utilities, hooks, reducers, small components with mocked dependencies.

• Integration tests

  • Purpose: Verify multiple units working together (e.g., function + DB/client, component + context/provider) without spinning up the full app.
  • Where: Each package under tests/integration (e.g., backend/shared/tests/integration, web/tests/integration).
  • Runner: Jest (configured via root jest.config.js).
  • Naming: *.integration.test.ts (or .tsx for React in web).
  • When to use: Boundaries between modules, real serialization/parsing, API handlers with mocked network/DB, component trees with providers.

• End-to-End (E2E) tests

  • Purpose: Validate real user flows across the full stack.
  • Where: Top-level tests/e2e with separate areas for web and backend.
  • Runner: Playwright (see root playwright.config.ts, testDir: ./tests/e2e).
  • Naming: *.e2e.spec.ts.
  • When to use: Critical journeys (signup, login, checkout), cross-service interactions, smoke tests for deployments.

Quick commands

# Jest (unit + integration)
yarn test

# Playwright (E2E)
yarn test:e2e

Where to put test files

# Config
jest.config.js (for unit and integration tests)
playwright.config.ts (for e2e tests)

# Top-level End-to-End (Playwright)
tests/
├── e2e/
│   ├── web/
│   │   ├── pages/
│   │   └── specs/
│   │       └── example.e2e.spec.ts
│   └── backend/
│       └── specs/
│           └── api.e2e.spec.ts
└── reports/
    └── playwright-report/

# Package-level Unit & Integration (Jest)
backend/
├── api/
│   ├── src/
│   └── tests/
│       ├── unit/
│       │   └── example.unit.test.ts
│       └── integration/
│           └── example.integration.test.ts
├── email/
│   └── tests/
│       ├── unit/
│       └── integration/
└── shared/
    └── tests/
        ├── unit/
        └── integration/

common/
└── tests/
    ├── unit/
    │   └── example.unit.test.ts
    └── integration/
        └── example.integration.test.ts

web/
└── tests/
    ├── unit/
    │   └── example.unit.test.tsx
    └── integration/
        └── example.integration.test.tsx

• End-to-End tests live under tests/e2e and are executed by Playwright. The root playwright.config.ts sets testDir to ./tests/e2e.
• Unit and integration tests live in each package’s tests folder and are executed by Jest via the root jest.config.js projects array.
• Naming:
  • Unit: *.unit.test.ts (or .tsx for React in web)
  • Integration: *.integration.test.ts
  • E2E (Playwright): *.e2e.spec.ts

Best Practices

• Test Behavior, Not Implementation. Don’t test internal state or function calls unless you’re testing utilities or very critical behavior.
• Use msw to Mock APIs. Don't manually mock fetch—use msw to simulate realistic behavior, including network delays and errors.
• Don’t Overuse Snapshots. Snapshots are fragile and often meaningless unless used sparingly (e.g., for JSON response schemas).
• Prefer userEvent Over fireEvent. It simulates real user interactions more accurately.
• Avoid Testing Next.js Internals . You don’t need to test getStaticProps, getServerSideProps themselves-test what they render.
• Don't test just for coverage. Test to prevent regressions, document intent, and handle edge cases.
• Don't write end-to-end tests for features that change frequently unless absolutely necessary.

Jest Unit Testing Guide

This guide provides guidelines and best practices for writing unit tests using Jest in this project. Following these standards ensures consistency, maintainability, and comprehensive test coverage.

Best Practices

1. Isolate a function route - Each test should focus on one thing that can affect the function outcome
2. Keep tests independent - Tests should not rely on the execution order
3. Use meaningful assertions - Assert that functions are called, what they are called with and the results
4. Avoid testing implementation details - Focus on behavior and outputs
5. Mock external dependencies - Isolate the unit being tested

Running Tests

# Run all tests
yarn test

# Run specific test file
yarn test path/to/test.unit.test.ts

Test Standards

• Test file names should convey what to expect
  • Follow the pattern: <exact-filename>.[unit,integration].test.ts. Examples:
    • filename.unit.test.ts
    • filename.integration.test.ts
• Group related tests using describe blocks
• Use descriptive test names that explain the expected behavior.
  • Follow the pattern: "should expected behavior [relevant modifier]". Examples:
    • should ban user [with matching user id]
    • should ban user [with matching user name]

Mocking

Mocking means replacing a real dependency (like a module, function, API client, timer, or browser API) with a controllable test double so your test can run quickly and deterministically, without calling the real thing. In unit tests we use mocks to isolate the unit under test; in integration tests we selectively mock only the expensive or unstable edges (e.g., network, filesystem) while exercising real collaborations.

What to mock vs not to mock

• Mock: network/HTTP calls, databases/ORM clients, email/SMS providers, time and randomness (Date, timers, Math.random), browser APIs that are hard to reproduce in Node (e.g., localStorage, IntersectionObserver).
• Prefer real: pure functions, small utilities, reducers/selectors, simple components; let their real logic run so tests actually verify behavior.
• Don’t over-mock: If you mock everything, you only test your mocks. Keep integration tests that hit real boundaries inside the process.

Common test doubles

• Stub: a function that returns a fixed value (no assertions on how it was used).
• Spy: records how a function was called (calls count/args); may optionally change behavior.
• Mock: a spy with expectations about how it must be called; in Jest, jest.fn() and jest.spyOn() produce mock functions you can assert on.
• Fake: a lightweight in-memory implementation (e.g., an in-memory repo) used instead of the real service.

Jest quick reference

• Module mock: jest.mock('path/to/module') to replace all exports with mock functions. Control behavior with (exportedFn as jest.Mock).mockReturnValue(...) or .mockResolvedValue(...) for async.
• Function mock: const fn = jest.fn(); set behavior with .mockReturnValue, .mockImplementation.
• Spy on existing method: const spy = jest.spyOn(obj, 'method') and optionally spy.mockImplementation(...).
• Timers/time: jest.useFakeTimers(); jest.setSystemTime(new Date('2024-01-01')); and advance with jest.advanceTimersByTime(ms); finally jest.useRealTimers().
• Clearing: jest.clearAllMocks() (between tests) vs jest.resetAllMocks() (reset implementations) vs jest.restoreAllMocks() (restore spied originals).

When writing mocks, assert both outcome and interaction:

• Outcome: what your function returned or what side-effect occurred.
• Interaction: that dependencies were called the expected number of times and with the right arguments.

Why mocking is important?

• Isolation - Test your code independently of databases, APIs, and external systems. Tests only fail when your code breaks, not when a server is down.
• Speed - Mocked tests run in milliseconds vs. seconds for real network/database calls. Run your suite constantly without waiting.
• Control - Easily simulate edge cases like API errors, timeouts, or rare conditions that are difficult to reproduce with real systems.
• Reliability - Eliminate unpredictable failures from network issues, rate limits, or changing external data. Same inputs = same results, every time.
• Focus - Verify your function's logic and how it uses its dependencies, without requiring those dependencies to actually work yet.

Use jest.mock()

Jest automatically hoists all jest.mock() calls to the top of the file before imports are evaluated. To maintain clarity and align with best practices, explicitly place jest.mock() calls at the very top of the file.

Modules mocked this way automatically return undefined, which is useful for simplifying tests. If a module or function’s return value isn’t used, there’s no need to mock it further.

//Function and module mocks
jest.mock('path/to/module');

//Function and module imports
import {functionUnderTest} from "path/to/function"
import {module} from "path/to/module"

describe('functionUnderTest', () => {
  //Setup
  beforeEach(() => {
    //Run before each test
    jest.resetAllMocks(); // Resets any mocks from previous tests
  });
  afterEach(() => {
    //Run after each test
    jest.restoreAllMocks(); // Cleans up between tests
  });

  describe('when given valid input', () => {
    it('should describe what is being tested', async () => {
      //Arrange: Setup test data
      const mockData = 'test';

      //Act: Execute the function under test
      const result = myFunction(mockData);

      //Assert: Verify the result
      expect(result).toBe('expected');
    });
  });

  describe('when an error occurs', () => {
    //Test cases for errors
  });
});

Modules

When mocking modules it's important to verify what was returned if applicable, the amount of times said module was called and what it was called with.

//functionFile.ts
import { module as mockedDep } from "path/to/module"

export const functionUnderTest = async (param) => {
    return await mockedDep(param);
};

//testFile.unit.test.ts
import { functionUnderTest } from "path/to/function";
import { module as mockedDep } from "path/to/module";
jest.mock('path/to/module');

/**
 * Inside the test case
 * We create a mock for any information passed into the function that is being tested
 * and if the function returns a result we create a mock to test the result
 */
const mockParam = "mockParam"
const mockReturnValue = "mockModuleValue"

/**
 * use .mockResolvedValue when handling async/await modules that return values
 * use .mockReturnValue when handling non async/await modules that return values
 */
(module as jest.Mock).mockResolvedValue(mockReturnValue);

const result = await functionUnderTest(mockParam);

expect(result).toBe(mockReturnValue);
expect(module).toBeCalledTimes(1);
expect(module).toBeCalledWith(mockParam);

Use namespace imports when you want to import everything a module exports under a single name.

//moduleFile.ts
export const module = async (param) => {
    const value = "module"
    return value
};

export const moduleTwo = async (param) => {
    const value = "moduleTwo"
    return value
};

//functionFile.ts
import { module, moduleTwo } from "path/to/module"

export const functionUnderTest = async (param) => {
    const mockValue = await moduleTwo(param)
    const returnValue = await module(mockValue)
    return returnValue;
};

//testFile.unit.test.ts
jest.mock('path/to/module');

/**
 * This creates an object containing all named exports from ./path/to/module
 */
import * as mockModule from "path/to/module"

(mockModule.module as jest.Mock).mockResolvedValue(mockReturnValue);

When mocking modules, you can use jest.spyOn() instead of jest.mock().

• jest.mock() mocks the entire module, which is ideal for external dependencies like Axios or database clients.
• jest.spyOn() mocks specific methods while keeping the real implementation for others. It can also be used to observe how a real method is called without changing its behavior.
  • also replaces the need to have jest.mock() at the top of the file.

//testFile.unit.test.ts
import * as mockModule from "path/to/module"

//Mocking the return value of the module
jest.spyOn(mockModule, 'module').mockResolvedValue(mockReturnValue);

//Spying on the module to check functionality
jest.spyOn(mockModule, 'module');

//You can assert the module functionality with both of the above exactly like you would if you used jest.mock()
expect(mockModule.module).toBeCalledTimes(1);
expect(mockModule.module).toBeCalledWith(mockParam);

Dependencies

Mocking dependencies allows you to test your code’s logic in isolation, without relying on third-party services or external functionality.

//functionFile.ts
import { dependency } from "path/to/dependency"

export const functionUnderTest = async (param) => {
    const depen = await dependency();
    const value = depen.module();

    return value;
};

//testFile.unit.test.ts
jest.mock('path/to/dependency');

import { dependency } from "path/to/dependency"

describe('functionUnderTest', () => {
    /**
     * Because the dependency has modules that are used we need to 
     * create a variable outside of scope that can be asserted on
     */
    let mockDependency = {} as any;
    beforeEach(() => {
        mockDependency = {
            module: jest.fn(),
        };
        jest.resetAllMocks(); // Resets any mocks from previous tests
    });
    afterEach(() => {
        //Run after each test
        jest.restoreAllMocks(); // Cleans up between tests
    });

    //Inside the test case
    (mockDependency.module as jest.Mock).mockResolvedValue(mockReturnValue);

    expect(mockDependency.module).toBeCalledTimes(1);
    expect(mockDependency.module).toBeCalledWith(mockParam);
});

Error checking

//function.ts
const result = await functionName(param);

if (!result) {
    throw new Error (403, 'Error text', error);
};

//testFile.unit.test.ts
const mockParam = {} as any;

//This will check only the error message
expect(functionName(mockParam))
    .rejects
    .toThrowError('Error text');

//This will check the complete error
try {
    await functionName(mockParam);
    fail('Should have thrown');
} catch (error) {
    const functionError = error as Error;
    expect(functionError.code).toBe(403);
  expect(functionError.message).toBe('Error text');
    expect(functionError.details).toBe(mockParam);
    expect(functionError.name).toBe('Error');
}

//For console.error types
console.error('Error message', error);

//Use spyOn to mock
const errorSpy = jest.spyOn(console, 'error').mockImplementation(() => {});

expect(errorSpy).toHaveBeenCalledWith(
    'Error message',
    expect.objectContaining({name: 'Error'}) //The error 'name' refers to the error type
);

Mocking array return value

//arrayFile.ts
const exampleArray = [ 1, 2, 3, 4, 5 ];

const arrayResult = exampleArray.includes(2);

//testFile.unit.test.ts

//This will mock 'includes' for all arrays and force the return value to be true
jest.spyOn(Array.prototype, 'includes').mockReturnValue(true);

// ---
//This will specify which 'includes' array to mock based on the args passed into the .includes()
jest.spyOn(Array.prototype, 'includes').mockImplementation(function(value) {
  if (value === 2) {
    return true;
  }
  return false;
});

Playwright (E2E) Testing Guide

TODO