mockFirebase.js

const mockInitializeApp = jest.fn();
const mockCert = jest.fn();

const defaultOptions = {
  includeIdsInData: false,
  mutable: false,
};

class FakeAuth {
  constructor() {
  }
  createUser() {
    return Promise.resolve('OK')
  }
}


const firebaseStub = (overrides, options = defaultOptions) => {
  const { FakeFirestore } = require('firestore-jest-mock');

  // Prepare namespaced classes
  function firestoreConstructor() {
    return new FakeFirestore(overrides.database, options);
  }

  firestoreConstructor.Query = FakeFirestore.Query;
  firestoreConstructor.CollectionReference = FakeFirestore.CollectionReference;
  firestoreConstructor.DocumentReference = FakeFirestore.DocumentReference;
  firestoreConstructor.FieldValue = FakeFirestore.FieldValue;
  firestoreConstructor.Timestamp = FakeFirestore.Timestamp;
  firestoreConstructor.Transaction = FakeFirestore.Transaction;
  firestoreConstructor.FieldPath = FakeFirestore.FieldPath;

  // The Firebase mock
  return {
    initializeApp: mockInitializeApp,

    credential: {
      cert: mockCert,
    },

    auth() {
      return new FakeAuth();
    },

    firestore: firestoreConstructor,
  };
};

const mockFirebase = (overrides = {}, options = defaultOptions) => {
  mockModuleIfFound('firebase', overrides, options);
  mockModuleIfFound('firebase-admin', overrides, options);
};

function mockModuleIfFound(moduleName, overrides, options) {
  try {
    require.resolve(moduleName);
    jest.doMock(moduleName, () => firebaseStub(overrides, options));
  } catch (e) {
    // eslint-disable-next-line no-console
    console.info(`Module ${moduleName} not found, mocking skipped.`);
  }
}