webmaxru/bpm-counter/azure-functions-test-mocking

function loadHandler(mockOverrides) {
  jest.resetModules(); // Clear stale module-scope state
  let handler;
  jest.isolateModules(() => {
    jest.doMock('applicationinsights', () => ({ /* mocks */ }));
    jest.doMock('@azure/cosmos', () => ({ /* mocks */ }), { virtual: true });
    handler = require('./index');
  });
  return handler;
}
// Variant: test what happens when setup() THROWS at module load
function loadHandlerWithSetupCrash() {
  jest.resetModules();
  let handler;
  jest.isolateModules(() => {
    jest.doMock('applicationinsights', () => ({
      setup: jest.fn(() => { throw new Error('Init failed'); }),
      defaultClient: null,
    }));
    jest.doMock('@azure/cosmos', () => ({ /* mocks */ }), { virtual: true });
    handler = require('./index');
  });
  return handler;
}

function createMockContext(overrides = {}) {
  const log = jest.fn();
  log.error = jest.fn();
  log.warn = jest.fn();
  log.info = jest.fn();
  return {
    log, res: null, bindings: {},
    traceContext: { traceparent: 'test-trace-id' },
    done: jest.fn(),
    ...overrides,
  };
}

function base64Encode(obj) {
  return Buffer.from(JSON.stringify(obj)).toString('base64');
}
// Test: valid, missing, garbage base64, valid-base64-of-invalid-JSON

test('early return triggers ALL expected side effects', async () => {
  const handler = loadHandler();
  const context = createMockContext();
  const req = createMockReq({ isCorrect: true }); // missing bpm
  await handler(context, req);
  expect(context.res.status).toBe(400);        // correct status
  expect(mockTrackException).toHaveBeenCalled(); // exception tracked
  expect(mockCosmosCreate).not.toHaveBeenCalled(); // NO database write
  expect(mockTrackEvent).not.toHaveBeenCalled();   // NO success event
});