unit-tests

name	unit-tests
description	Expert unit test engineer for MMO FES Function App. Use when: writing unit tests, updating tests for code changes, fixing failing tests, improving code coverage, fixing SonarQube issues.
license	OGL-UK-3.0
metadata	{"author":"mmo-fes","version":"1.0"}

Function App — Unit Tests Skill

Expert in writing and maintaining unit tests for MMO FES Azure Functions.

When to Use

• Writing unit tests for new or modified functions
• Fixing failing tests after code changes
• Improving code coverage to meet thresholds
• Fixing SonarQube issues or code smells

Coverage Requirements

• Branches: 90%
• Functions: 90%
• Lines: 90%
• Statements: 90%
• Run tests: npm test
• Run CI tests: npm run test:ci

Test Framework & Tools

• Jest as test runner with jest-junit reporter
• Test files colocated in __tests__/ or alongside source

Mocking Patterns

Azure Function Context

const mockContext = {
  log: jest.fn(),
  bindings: {},
  executionContext: { functionName: 'myFunction' },
  operationId: 'test-op-id'
};

Timer Trigger

const mockTimer = {
  IsPastDue: false,
  Schedule: { AdjustForDST: true }
};

Config Override

const overrideConfig = {
  instrumentationKey: 'test-key',
  apiUrl: 'http://localhost:3000'
};

await func(mockContext, mockTimer, overrideConfig);

setTimeout (Critical for Retry Tests)

jest.useFakeTimers();
// trigger retry
jest.advanceTimersByTime(retryDelay);
jest.useRealTimers();

Axios

jest.mock('axios');
const mockedAxios = axios;
mockedAxios.put.mockResolvedValue({ status: 200, data: {} });
// For retry tests:
mockedAxios.put
  .mockRejectedValueOnce(new Error('fail'))
  .mockResolvedValueOnce({ status: 200, data: {} });

What to Test

1. Happy path — function executes successfully with valid timer/HTTP trigger
2. IsPastDue — verify late execution is logged
3. Retry logic — verify exponential backoff delays and max retry limit
4. App Insights — verify events and requests are tracked
5. Error handling — verify errors are caught, logged, and re-thrown appropriately
6. Config override — verify overrideConfig merges correctly

SonarQube Issue Resolution

When fixing SonarQube issues, NEVER modify functionality. If existing tests fail after a fix, revert it.

Workflow

1. Identify the function(s) that need tests
2. Create mock context, timer, and config
3. Write tests following Arrange/Act/Assert pattern
4. Run npm test and check coverage output
5. If coverage below thresholds, add targeted tests for uncovered branches
6. Check problems tab for SonarQube issues