Example of Firebase emulator unit tests and seed Firestore data

firebase.json

{
  "firestore": {
    "rules": "firestore.rules",
    "indexes": "firestore.indexes.json"
  },
  "emulators": {
    "firestore": {
      "port": 8080
    }
  }
}

firestore.rules

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
     match rows/{rowId} {
        allow read: if request.auth.uid == resource.data.owner;
     }
  }
}

seed.json

{
  "rows/foo": {
    "owner": "kato", "score": 10
  },
  "rows/bar": {
    "owner": "puf", "score": 20
  }
}

test.ts

/// <reference path='../node_modules/mocha-typescript/globals.d.ts' />

import * as firebase from "@firebase/testing";

/*
 * ============
 *    Setup
 * ============
 */
const port = require("./firebase.json").emulators.firestore.port;
const projectId = "gvcassistant-staging";
const coverageUrl = `http://localhost:${port}/emulator/v1/projects/${projectId}:ruleCoverage.html`;
const fs = require("fs");
const rules = fs.readFileSync("./firestore.rules", "utf8");
const seed = require('./seed.json');

/**
 * Creates a new app with authentication data matching the input.
 *
 * @param {object} auth the object to use for authentication (typically {uid: some-uid})
 * @return {object} the app.
 */
function authedApp(auth: object) {
  return firebase
    .initializeTestApp({ projectId, auth })
    .firestore();
}

async function resetData() {
  await firebase.clearFirestoreData({ projectId });
  const db = firebase.initializeAdminApp({projectId}).firestore();
  const promises = Object.entries(seed).map(entry => db.doc(entry[0]).set(entry[1]));
  await Promise.all(promises);
}

/*
 * ============
 *  Test Cases
 * ============
 */
before(async () => {
  await firebase.loadFirestoreRules({ projectId, rules });
});

beforeEach(resetData);

after(async () => {
  await Promise.all(firebase.apps().map(app => app.delete()));
  console.log(`View rule coverage information at ${coverageUrl}\n`);
});

@suite
class MyApp {
  @test
  async "can access rows I own"() {
    const db = authedApp({uid: "kato"});
    const doc = db.doc("rows/foo");
    await firebase.assertSucceeds(doc.get());
  }

  @test
  async "cannot access rows I do not own"() {
    const db = authedApp({uid: "kato"});
    const doc = db.doc("rows/bar");
    await firebase.assertFails(doc.get());
  }
}

@Dwiga your question is not related to this example, which covers Firestore unit tests in the emulator. Try Stack Overflow or Reddit.