Mocking fetch

// jest.config.js
const { defaults } = require("jest-config");

module.exports = {
    preset: 'ts-jest',
    testEnvironment: "miniflare",
    moduleFileExtensions: ["mjs", ...defaults.moduleFileExtensions],
};

// src/worker.ts

export default {
  async fetch(cfRequest: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    const url = new URL('https://example.com');
    return sendRequestToAPI(url, { bodyStuff: 'here' }, env, cfRequest, ctx);
    const resp = await fetch('example.com');
  },
};

// src/helpers.ts
export const sendToApi = async (
  url: URL,
  body: any,
  env: Env,
  cfRequest: Request,
  ctx: ExecutionContext
): Promise<Response> => {
  const request = {
    body: JSON.stringify(body),
    method: 'POST'
  };
    const response = await fetch(url, request);
    if (response.status !== 200) {
        return new Response('Bad', { status: 500 });
    } else {
        return new response('Good', {status: 200});
    }
}