online1.test.ts

import functions from "firebase-functions-test";
import * as admin from "firebase-admin";
import * as path from "path";

// you can check all these information in firebase console/settings
const projectConfig = {
  projectId: "projectId",
  databaseURL: "databaseURL"
};

// you should pass projectConfig and path to serviceAccountKey like this
// path.resolve defaults to directory where you're executing test command
// for my case, it's functions directory
const testEnv = functions(projectConfig, path.resolve("service-key.json"));