wagtail/client/tests/mock-fetch.js

// Mocking the global.fetch and global.Headers
global.fetch = jest.fn();
global.Headers = jest.fn();

// Helper to mock a success response.
fetch.mockResponseSuccess = (body) => {
  fetch.mockImplementationOnce(() => Promise.resolve({
    json: () => Promise.resolve(JSON.parse(body)),
    status: 200,
    statusText: 'OK',
  }));
};

// Helper to mock a failure response.
fetch.mockResponseFailure = () => {
  fetch.mockImplementationOnce(() => Promise.resolve({
    status: 500,
    statusText: 'Internal Error',
  }));
};

fetch.mockResponseCrash = () => {
  fetch.mockImplementationOnce(() => Promise.reject({
    status: 500,
    statusText: 'Internal Error',
  }));
};

// Helper to mock a timeout response.
fetch.mockResponseTimeout = () => {
  fetch.mockImplementationOnce(() => {
    const timeout = 1000;

    return new Promise((resolve) => {
      setTimeout(() => setTimeout(resolve, timeout), timeout);
    });
  });
};