Cannot find module 'firebase-admin/app' from ""

[yun8boo]

When using Node.js SDK Admin SDK v10 in Nest.js, the test gets angry that the module is not found

    Cannot find module 'firebase-admin/app' from 'libs/firebase-admin/firebase-admin.service.ts'

    Require stack:
      libs/firebase-admin/firebase-admin.service.ts
      libs/firebase-admin/auth/auth.module.ts
      libs/firebase-admin/auth/auth.service.spec.ts

      1 | import { Injectable, Logger } from '@nestjs/common';
      2 | import { ConfigService } from '@nestjs/config';
    > 3 | import { ServiceAccount, initializeApp, cert, getApps } from 'firebase-admin/app';
        | ^
      4 | import { getAuth } from 'firebase-admin/auth';
      5 |
      6 | @Injectable()

      at Resolver.resolveModule (../node_modules/jest-resolve/build/resolver.js:324:11)
      at Object.<anonymous> (libs/firebase-admin/firebase-admin.service.ts:3:1)

[MILLERMARRU]

This error comes from Jest not knowing how to handle Firebase Admin SDK v10+'s modular package exports ("exports" field in package.json). Jest's default module resolver doesn't follow the exports map, so firebase-admin/app can't be found.

Fix for Jest + NestJS (or any Node project)

Add moduleNameMapper to your Jest config to manually map the modular imports:

// jest.config.js
module.exports = {
  // ... your existing config
  moduleNameMapper: {
    '^firebase-admin/app$': '<rootDir>/node_modules/firebase-admin/lib/app/index.js',
    '^firebase-admin/auth$': '<rootDir>/node_modules/firebase-admin/lib/auth/index.js',
    '^firebase-admin/firestore$': '<rootDir>/node_modules/firebase-admin/lib/firestore/index.js',
    '^firebase-admin/messaging$': '<rootDir>/node_modules/firebase-admin/lib/messaging/index.js',
    '^firebase-admin/storage$': '<rootDir>/node_modules/firebase-admin/lib/storage/index.js',
    // Add other subpackages as needed
  },
};

Alternative: use transformIgnorePatterns

If you're using ESM transforms, add Firebase Admin to the exceptions list:

// jest.config.js
module.exports = {
  transformIgnorePatterns: [
    'node_modules/(?!(firebase-admin)/)',
  ],
};

For NestJS projects specifically

NestJS uses jest.config.js at the root and sometimes a separate one inside apps/. Make sure the fix is in the config that Jest actually loads for the failing test file.

Also verify your tsconfig.json has "moduleResolution": "node16" or "bundler" — older "node" resolution doesn't follow package exports either, which can cause the same error at compile time (not just test time).

Root cause

Firebase Admin SDK v10 switched to modular imports (following the firebase JS SDK pattern). Before v10, you imported everything from 'firebase-admin'. The new subpath imports (firebase-admin/app, firebase-admin/auth, etc.) rely on the exports field in package.json, which Jest < 28 ignores by default. Jest 28+ respects exports if you set "resolver": "jest-resolve" with "customExportConditions": ["node", "require"].