Nuxt 4 + Layers breaks Nuxt Test Utils

[wuiyang]

Environment

- Operating System: Linux
- Node Version:     v20.16.0
- Nuxt Version:     3.17.2
- CLI Version:      3.25.0
- Nitro Version:    2.11.11
- Package Manager:  [email protected]
- Builder:          -
- User Config:      modules, devtools, compatibilityDate
- Runtime Modules:  @nuxt/test-utils/[email protected]
- Build Modules:    -

Reproduction

Github repo: https://github.com/wuiyang/nuxt-layer-test-bug Stackblitz: https://stackblitz.com/~/github.com/wuiyang/nuxt-layer-test-bug

Describe the bug

When project root is using Nuxt 4 version (via config future.compatibilityVersion = 4), nuxt test utils would not work on layers within same project.

The unit test would run without console error log, but the test report would show there is an error:

TypeError: Cannot read properties of undefined (reading 'vueApp')

When project root is not using Nuxt 4 version, the nuxt test utils would work as expected. See reproduction repo:

• Github: https://github.com/wuiyang/nuxt-layer-test-bug/tree/working-without-nuxt-4
• Stackblitz: https://stackblitz.com/~/github.com/wuiyang/nuxt-layer-test-bug/tree/working-without-nuxt-4?file=package.json

Additional context

No response

Logs

abc@efac4cbfa0a5:/..../nuxt-layer-test-bug$ npx vitest run --coverage
 Vitest  "environmentMatchGlobs" is deprecated. Use "workspace" to define different configurations instead.
 HTML  Report is generated
       You can run npx vite preview --outDir ../test-reports/unit-test to see the test results.

[Archetipo95]

Looks like it's working fine

Node 22, pnpm 8

"devDependencies": {
    "@nuxt/test-utils": "^3.19.1",
    "@vitest/coverage-v8": "^3.1.4",
    "@vitest/ui": "^3.1.4",
    "@vue/test-utils": "^2.4.6",
    "happy-dom": "^17.5.6",
    "nuxt": "^3.17.4",
    "vitest": "^3.1.4",
    "vite": "^6.3.5",
    "vue": "^3.5.16"
  },