firebase-admin/app module can't be resolved in jest unit test (NestJS Application)

Question

I'm writing Unit-Tests for a NESTJS Application. In the normal app-code the module can be resolved and everything works just fine, but in the unit tests i get this error when importing { initializeApp, applicationDefault } from 'firebase-admin/app':

Node Version: v16.13.1 - Also tested on: v12 and v17

NestJS Version: v8.1.2

Firebase-Admin: v10.0.0

Edit - My package.json file:

{
"name": "flightschool",
  "version": "0.0.1",
  "description": "",
  "author": "",
  "private": true,
  "license": "UNLICENSED",
  "scripts": {
    "prebuild": "rimraf dist",
    "build": "nest build",
    "format": "prettier --write \"src/**/*.ts\" \"test/**/*.ts\"",
    "start": "nest start",
    "start:dev": "nest start --watch",
    "start:debug": "nest start --debug --watch",
    "start:prod": "node dist/main",
    "lint": "eslint \"{src,apps,libs,test}/**/*.ts\" --fix",
    "test": "jest",
    "test:watch": "jest --watch",
    "test:cov": "jest --coverage",
    "test:debug": "node --inspect-brk -r tsconfig-paths/register -r ts-node/register node_modules/.bin/jest --runInBand",
    "test:e2e": "jest --config ./test/jest-e2e.json"
  },
  "dependencies": {
    "@nestjs/common": "^8.0.0",
    "@nestjs/core": "^8.0.0",
    "@nestjs/passport": "^8.0.1",
    "@nestjs/platform-express": "^8.0.0",
    "@nestjs/swagger": "^5.1.0",
    "@nestjs/typeorm": "^8.0.2",
    "firebase": "^9.1.2",
    "firebase-admin": "^10.0.0",
    "mysql2": "^2.3.0",
    "passport": "^0.4.1",
    "passport-local": "^1.0.0",
    "reflect-metadata": "^0.1.13",
    "rimraf": "^3.0.2",
    "rxjs": "^7.2.0",
    "swagger-ui-express": "^4.1.6",
    "typeorm": "^0.2.38"
  },
  "devDependencies": {
    "@nestjs/cli": "^8.0.0",
    "@nestjs/schematics": "^8.0.0",
    "@nestjs/testing": "^8.0.0",
    "@types/express": "^4.17.13",
    "@types/jest": "^27.0.1",
    "@types/node": "^16.0.0",
    "@types/passport-local": "^1.0.34",
    "@types/supertest": "^2.0.11",
    "@typescript-eslint/eslint-plugin": "^4.28.2",
    "@typescript-eslint/parser": "^4.28.2",
    "eslint": "^7.30.0",
    "eslint-config-prettier": "^8.3.0",
    "eslint-plugin-prettier": "^3.4.0",
    "jest": "^27.0.6",
    "prettier": "^2.3.2",
    "supertest": "^6.1.3",
    "ts-jest": "^27.0.3",
    "ts-loader": "^9.2.3",
    "ts-node": "^10.0.0",
    "tsconfig-paths": "^3.10.1",
    "typescript": "^4.3.5"
  },
  "jest": {
    "moduleFileExtensions": [
      "js",
      "json",
      "ts"
    ],
    "rootDir": "src",
    "testRegex": ".*\\.spec\\.ts$",
    "transform": {
      "^.+\\.(t|j)s$": "ts-jest"
    },
    "collectCoverageFrom": [
      "**/*.(t|j)s"
    ],
    "coverageDirectory": "../coverage",
    "testEnvironment": "node"
  }
}

Answer 1

This is a known issue with Jest. See https://github.com/facebook/jest/issues/9771 and https://github.com/firebase/firebase-admin-node/issues/1465. You can find some workarounds in the above issues.