mockFetch.ts

type AnyObj = { [key: string]: any };

const M = (
  globalWindow: AnyObj,
  headerParams: { [key: string]: string },
  transferList: { url: string, response: AnyObj }[]
) => {
  const cacheFetch = globalWindow.fetch;
  delete globalWindow.fetch;
  const headers = new Headers();
  Object.entries(headerParams).forEach(([k, v]) => headers.append(k, v))
  globalWindow.fetch = (calledUrl: string, calledOpt: AnyObj) => {
    for (let { url, response } of transferList) {
      if (calledUrl === url) {
        return Promise.resolve({
          headers, status: 200, ok: true,
          json: async () => Promise.resolve(response),
        });
      }
    }
    return cacheFetch(calledUrl, calledOpt);
  };
};

export default M;