jest - detect unmocked network requests

setupTests.js

// from @kentcdodds
beforeEach(() => {
  jest.spyOn(window, 'fetch').mockImplementation((...args) => {
    console.warn('window.fetch is not mocked for this call', ...args);
    throw new Error('This must be mocked!');
  });
});

afterEach(() => {
  window.fetch.mockRestore();
});