message: fix broken fetch tests
diff: import { of } from 'rxjs';
  import { take } from 'rxjs/operators';
  import { fetchExchange } from './fetch';
  +import { Exchange } from '../types';
  import { queryOperation, subscriptionOperation } from '../test-utils';
  const fetch = (global as any).fetch as jest.Mock;
  @@ -18,13 +19,18 @@ const repsonse = {
  },
  };
  +const args = {
  + forward: jest.fn(),
  + subject: {},
  +} as any;
  +
  it('should return response data from fetch', async () => {
  fetch.mockResolvedValue({
  status: 200,
  json: jest.fn().mockResolvedValue(repsonse),
  });
  - const data = await fetchExchange(jest.fn())(of(queryOperation))
  + const data = await fetchExchange(args)(of(queryOperation))
  .pipe(take(1))
  .toPromise();
  expect(data).toMatchSnapshot();
  @@ -36,7 +42,7 @@ it('should return error data from fetch', async () => {
  json: jest.fn().mockResolvedValue(repsonse),
  });
  - const data = await fetchExchange(jest.fn())(of(queryOperation))
  + const data = await fetchExchange(args)(of(queryOperation))
  .pipe(take(1))
  .toPromise();
  expect(data).toMatchSnapshot();
  @@ -44,7 +50,7 @@ it('should return error data from fetch', async () => {
  it('should throw error when operationName is subscription', async () => {
  try {
  - await fetchExchange(jest.fn())(of(subscriptionOperation)).toPromise();
  + await fetchExchange(args)(of(subscriptionOperation)).toPromise();
  fail();
  } catch (err) {
  expect(err).toMatchSnapshot();
  