typescript-testing

name	typescript-testing
description	Mandatory testing conventions for TypeScript stacks (Vitest for CLI/SDK/Website/CDK). Use for unit, integration, or E2E tests with Vitest or Playwright.

Testing Conventions (TypeScript)

This skill defines the MANDATORY testing conventions for TypeScript projects. These are rules, not guidelines.

---

Documentation Rules

NO Comments Except AAA Markers

• Do NOT write explanatory comments: code must be self-explanatory
• Only // Arrange, // Act, // Assert comments are allowed in tests
• The test name Should_X_When_Y already documents the intent

Exception: SDK public API: Code under src/sdks/*/ consumed by external developers (facade classes, public entry points) SHOULD have JSDoc with usage examples. This exception does not apply to tests or internal helpers.

---

Stacks Overview

Stack	Test Runner	Location
CLI / Core	Vitest	tests/envilder/
Node.js SDK	Vitest	tests/sdks/nodejs/
Website	Vitest	tests/website/
CDK (IaC)	Vitest	tests/iac/
E2E	Vitest + TestContainers	e2e/

---

Core Principles

1. AAA Pattern (Arrange – Act – Assert)

ALL tests MUST follow the AAA pattern, separated by inline comments.

Rules

• Each phase MUST be separated with comments
• Never mix phases
• Each comment (// Arrange, // Act, // Assert) appears AT MOST ONCE per test: if you need two actions or two asserts, write two tests
• Act = one single invocation on the SUT. Multiple statements in Act only if they are genuinely part of the same logical action (rare and exceptional). Two independent operations = two tests.
• All assertions belong in Assert only. No expect() in Arrange or Act. If you feel tempted to assert in Arrange (precondition check), extract it to a separate test or use a guard clause that throws: not an assertion.
• AAA markers are mandatory in ALL tests: including structural guards, static completeness checks, and data validation tests. No exceptions.
• No if, switch, or conditional logic inside Arrange, Act, or Assert
• No try/catch/finally inside tests: use beforeEach/afterEach for teardown
• No // Act & Assert combined blocks: Act and Assert are ALWAYS separate
• For exceptions: expect(() => action()).toThrow() or await expect(asyncAction()).rejects.toThrow()
• Omit comment if section is empty
• If a test needs branching, split it into separate tests (one per scenario)

Vitest Example

it('Should_GenerateEnvFile_When_ValidParametersProvided', async () => {
  // Arrange
  mockStore.getMapping.mockResolvedValue({ KEY: '/ssm/path' });
  mockProvider.getSecret.mockResolvedValue('value');

  // Act
  await sut.handle(command);

  // Assert
  expect(mockStore.saveEnvironment).toHaveBeenCalled();
});

---

2. Test Naming Convention

Test names MUST follow exactly:

Should_{ExpectedBehavior}_When_{Condition}

Rules

• PascalCase for both parts
• NO natural language sentences in it() descriptions
• NO vague names (Should_Work, TestHandler)
• NO missing When clause

Good Examples

Test Name	Scenario
Should_ThrowError_When_SSMParameterIsNotFound	Error path
Should_ReturnMaskedValue_When_SecretIsLoaded	Success path
Should_ReturnEmptyMap_When_NoMappingsExist	Edge case

---

Variable Naming (MANDATORY)

Purpose	Name
Subject under test	sut
Expected value	expected
Actual result	actual

No creativity allowed here.

---

Mocking (Vitest)

Port Test Doubles

const mockProvider: ISecretProvider = {
  getSecret: vi.fn(),
};

const mockStore: IVariableStore = {
  getMapping: vi.fn(),
  saveEnvironment: vi.fn(),
};

const mockLogger: ILogger = {
  info: vi.fn(),
  warn: vi.fn(),
  error: vi.fn(),
};

Controlling Behavior

vi.mocked(mockProvider.getSecret).mockResolvedValue('secret-value');
vi.mocked(mockProvider.getSecret).mockRejectedValue(new Error('not found'));
vi.mocked(mockStore.getMapping).mockResolvedValue({ KEY: '/path' });

Verifying Interactions

expect(mockProvider.getSecret).toHaveBeenCalledWith('/ssm/path');
expect(mockProvider.getSecret).toHaveBeenCalledTimes(1);
expect(mockLogger.info).toHaveBeenCalledWith(expect.stringContaining('success'));

---

Exception Testing

Act and Assert MUST be separate. Wrap the action in Act, assert in Assert.

✅ CORRECT: separate Act and Assert

it('Should_ThrowInvalidArgument_When_ProviderIsUnsupported', () => {
  // Arrange
  const config = { provider: 'unsupported' };

  // Act
  const act = () => createProvider(config);

  // Assert
  expect(act).toThrow(InvalidArgumentError);
});

✅ CORRECT: async exceptions

it('Should_ThrowParameterNotFound_When_SSMKeyIsMissing', async () => {
  // Arrange
  mockProvider.getSecret.mockRejectedValue(new ParameterNotFoundError('/missing'));

  // Act
  const act = sut.handle(command);

  // Assert
  await expect(act).rejects.toThrow(ParameterNotFoundError);
});

❌ FORBIDDEN: combined Act & Assert

it('Should_ThrowError_When_Invalid', () => {
  // Act & Assert   ← NEVER DO THIS
  expect(() => sut.handle(bad)).toThrow();
});

---

Test Class Structure

CLI / Core (Vitest + InversifyJS handlers)

describe('PullSecretsToEnvCommandHandler', () => {
  let sut: PullSecretsToEnvCommandHandler;
  let mockStore: { getMapping: Mock; saveEnvironment: Mock };
  let mockProvider: { getSecret: Mock };
  let mockLogger: { info: Mock; warn: Mock; error: Mock };

  beforeEach(() => {
    mockStore = { getMapping: vi.fn(), saveEnvironment: vi.fn() };
    mockProvider = { getSecret: vi.fn() };
    mockLogger = { info: vi.fn(), warn: vi.fn(), error: vi.fn() };
    sut = new PullSecretsToEnvCommandHandler(
      mockProvider,
      mockStore,
      mockLogger,
    );
  });

  it('Should_GenerateEnvFile_When_ValidParametersProvided', async () => {
    // Arrange
    mockStore.getMapping.mockResolvedValue({ KEY: '/ssm/path' });
    mockProvider.getSecret.mockResolvedValue('value');

    // Act
    await sut.handle(command);

    // Assert
    expect(mockStore.saveEnvironment).toHaveBeenCalled();
  });
});

Node.js SDK (Vitest, no DI)

describe('EnvilderClient', () => {
  it('Should_ResolveSecrets_When_ProviderReturnsValues', async () => {
    // Arrange
    const mockProvider: ISecretProvider = {
      getSecrets: vi.fn().mockResolvedValue(new Map([['KEY', 'value']])),
    };
    const sut = new EnvilderClient(mockProvider);

    // Act
    const actual = await sut.resolveSecrets(parsedMapFile);

    // Assert
    expect(actual.get('KEY')).toBe('value');
  });
});

CDK / IaC (Vitest)

describe('AppStack', () => {
  it('Should_CreateLambda_When_StackSynthesized', () => {
    // Arrange
    const app = new cdk.App();
    const stack = new AppStack(app, 'TestStack');

    // Act
    const actual = Template.fromStack(stack);

    // Assert
    actual.hasResourceProperties('AWS::Lambda::Function', {
      Runtime: 'nodejs22.x',
      Handler: 'index.handler',
    });
  });
});

---

Structural Guards

Tests that validate static data (i18n completeness, schema conformance, version consistency) still MUST use AAA markers. Arrange can be omitted if data is set up at the describe level:

it('Should_HaveNoMissingKeys_When_CatalanComparedToEnglish', () => {
  // Act
  const actual = enKeys.filter((k) => !caKeys.includes(k));

  // Assert
  expect(actual, 'Keys missing in ca.ts').toEqual([]);
});

---

Verification Commands

Context	Command
CLI / Core / Website	pnpm test
Node.js SDK	cd tests/sdks/nodejs && pnpm vitest run --reporter=verbose
CDK	cd tests/iac && pnpm test
CI parity	pnpm test:ci
Lint	pnpm lint
Format	pnpm format

---

Decision Points

• Pure domain logic → unit test at domain layer
• Handler orchestrating ports → mock ports with vi.fn()
• AWS integration semantics → E2E with LocalStack/TestContainers
• Static data consistency → structural guard
• CDK infrastructure → snapshot + fine-grained assertions

---

Completion Criteria

• Test names follow Should_<Expected>_When_<Condition>
• AAA markers present, each at most once
• sut, actual, expected used consistently
• Positive and negative paths covered
• Tests run green: pnpm test
• No lint regressions: pnpm lint