diff --git a/packages/nuxt/src/core/app.ts b/packages/nuxt/src/core/app.ts
index 7dbe752b69..1ae3d3b8e0 100644
--- a/packages/nuxt/src/core/app.ts
+++ b/packages/nuxt/src/core/app.ts
@@ -79,7 +79,8 @@ export async function generateApp (nuxt: Nuxt, app: NuxtApp, options: { filter?:
   await nuxt.callHook('app:templatesGenerated', app, filteredTemplates, options)
 }
 
-async function resolveApp (nuxt: Nuxt, app: NuxtApp) {
+/** @internal */
+export async function resolveApp (nuxt: Nuxt, app: NuxtApp) {
   // Resolve main (app.vue)
   if (!app.mainComponent) {
     app.mainComponent = await findPath(
diff --git a/packages/nuxt/test/app.test.ts b/packages/nuxt/test/app.test.ts
new file mode 100644
index 0000000000..e8f3e65644
--- /dev/null
+++ b/packages/nuxt/test/app.test.ts
@@ -0,0 +1,221 @@
+import { fileURLToPath } from 'node:url'
+import { mkdir, rm, writeFile } from 'node:fs/promises'
+import { randomUUID } from 'node:crypto'
+import { afterAll, describe, expect, it } from 'vitest'
+import { dirname, join, normalize, resolve } from 'pathe'
+import { withoutTrailingSlash } from 'ufo'
+import { createApp, resolveApp } from '../src/core/app'
+import { loadNuxt } from '../src'
+
+const repoRoot = withoutTrailingSlash(normalize(fileURLToPath(new URL('../../../', import.meta.url))))
+
+describe('resolveApp', () => {
+  afterAll(async () => {
+    await rm(resolve(repoRoot, '.fixture'), { recursive: true, force: true })
+  })
+  it('resolves app with default configuration', async () => {
+    const app = await getResolvedApp([])
+    expect(app).toMatchInlineSnapshot(`
+      {
+        "components": [],
+        "configs": [],
+        "dir": "<rootDir>",
+        "errorComponent": "<repoRoot>/packages/nuxt/src/app/components/nuxt-error-page.vue",
+        "extensions": [
+          ".js",
+          ".jsx",
+          ".mjs",
+          ".ts",
+          ".tsx",
+          ".vue",
+        ],
+        "layouts": {},
+        "mainComponent": "@nuxt/ui-templates/dist/templates/welcome.vue",
+        "middleware": [
+          {
+            "global": true,
+            "name": "manifest-route-rule",
+            "path": "<repoRoot>/packages/nuxt/src/app/middleware/manifest-route-rule.ts",
+          },
+        ],
+        "plugins": [
+          {
+            "mode": "client",
+            "src": "<repoRoot>/packages/nuxt/src/app/plugins/payload.client.ts",
+          },
+          {
+            "mode": "server",
+            "src": "<repoRoot>/packages/nuxt/src/app/plugins/revive-payload.server.ts",
+          },
+          {
+            "mode": "client",
+            "src": "<repoRoot>/packages/nuxt/src/app/plugins/revive-payload.client.ts",
+          },
+          {
+            "filename": "components.plugin.mjs",
+            "getContents": [Function],
+            "mode": "all",
+            "src": "<rootDir>/.nuxt/components.plugin.mjs",
+          },
+          {
+            "mode": "all",
+            "src": "<repoRoot>/packages/nuxt/src/head/runtime/plugins/unhead.ts",
+          },
+          {
+            "mode": "all",
+            "src": "<repoRoot>/packages/nuxt/src/app/plugins/router.ts",
+          },
+          {
+            "mode": "client",
+            "src": "<repoRoot>/packages/nuxt/src/app/plugins/chunk-reload.client.ts",
+          },
+          {
+            "mode": "client",
+            "src": "<repoRoot>/packages/nuxt/src/app/plugins/check-outdated-build.client.ts",
+          },
+        ],
+        "rootComponent": "<repoRoot>/packages/nuxt/src/app/components/nuxt-root.vue",
+        "templates": [],
+      }
+    `)
+  })
+
+  it('resolves layer plugins in correct order', async () => {
+    const app = await getResolvedApp([
+      // layer 1
+      'layer1/plugins/02.plugin.ts',
+      'layer1/plugins/object-named.ts',
+      'layer1/plugins/override-test.ts',
+      'layer1/nuxt.config.ts',
+      // layer 2
+      'layer2/plugins/01.plugin.ts',
+      'layer2/plugins/object-named.ts',
+      'layer2/plugins/override-test.ts',
+      'layer2/nuxt.config.ts',
+      // final (user) layer
+      'plugins/00.plugin.ts',
+      'plugins/object-named.ts',
+      {
+        name: 'nuxt.config.ts',
+        contents: 'export default defineNuxtConfig({ extends: [\'./layer2\', \'./layer1\'] })'
+      }
+    ])
+    const fixturePlugins = app.plugins.filter(p => !('getContents' in p) && p.src.includes('<rootDir>')).map(p => p.src)
+    // TODO: support overriding named plugins
+    expect(fixturePlugins).toMatchInlineSnapshot(`
+      [
+        "<rootDir>/layer1/plugins/02.plugin.ts",
+        "<rootDir>/layer1/plugins/object-named.ts",
+        "<rootDir>/layer1/plugins/override-test.ts",
+        "<rootDir>/layer2/plugins/01.plugin.ts",
+        "<rootDir>/layer2/plugins/object-named.ts",
+        "<rootDir>/layer2/plugins/override-test.ts",
+        "<rootDir>/plugins/00.plugin.ts",
+        "<rootDir>/plugins/object-named.ts",
+      ]
+    `)
+  })
+
+  it('resolves layer middleware in correct order', async () => {
+    const app = await getResolvedApp([
+      // layer 1
+      'layer1/middleware/global.global.ts',
+      'layer1/middleware/named-from-layer.ts',
+      'layer1/middleware/named-override.ts',
+      'layer1/nuxt.config.ts',
+      // layer 2
+      'layer2/middleware/global.global.ts',
+      'layer2/middleware/named-from-layer.ts',
+      'layer2/middleware/named-override.ts',
+      'layer2/plugins/override-test.ts',
+      'layer2/nuxt.config.ts',
+      // final (user) layer
+      'middleware/named-override.ts',
+      'middleware/named.ts',
+      {
+        name: 'nuxt.config.ts',
+        contents: 'export default defineNuxtConfig({ extends: [\'./layer2\', \'./layer1\'] })'
+      }
+    ])
+    const fixtureMiddleware = app.middleware.filter(p => p.path.includes('<rootDir>')).map(p => p.path)
+    // TODO: fix this
+    expect(fixtureMiddleware).toMatchInlineSnapshot(`
+      [
+        "<rootDir>/layer1/middleware/global.global.ts",
+        "<rootDir>/layer1/middleware/named-from-layer.ts",
+        "<rootDir>/layer1/middleware/named-override.ts",
+        "<rootDir>/middleware/named.ts",
+      ]
+    `)
+  })
+
+  it('resolves layer layouts correctly', async () => {
+    const app = await getResolvedApp([
+      // layer 1
+      'layer1/layouts/default.vue',
+      'layer1/layouts/layer.vue',
+      'layer1/nuxt.config.ts',
+      // layer 2
+      'layer2/layouts/default.vue',
+      'layer2/layouts/layer.vue',
+      'layer2/nuxt.config.ts',
+      // final (user) layer
+      'layouts/default.vue',
+      {
+        name: 'nuxt.config.ts',
+        contents: 'export default defineNuxtConfig({ extends: [\'./layer2\', \'./layer1\'] })'
+      }
+    ])
+    expect(app.layouts).toMatchInlineSnapshot(`
+      {
+        "default": {
+          "file": "<rootDir>/layouts/default.vue",
+          "name": "default",
+        },
+        "layer": {
+          "file": "<rootDir>/layer2/layouts/layer.vue",
+          "name": "layer",
+        },
+      }
+    `)
+  })
+})
+
+async function getResolvedApp (files: Array<string | { name: string, contents: string }>) {
+  const rootDir = resolve(repoRoot, 'node_modules/.fixture', randomUUID())
+  await mkdir(rootDir, { recursive: true })
+  for (const file of files) {
+    const filename = typeof file === 'string' ? join(rootDir, file) : join(rootDir, file.name)
+    await mkdir(dirname(filename), { recursive: true })
+    await writeFile(filename, typeof file === 'string' ? '' : file.contents || '')
+  }
+
+  const nuxt = await loadNuxt({ cwd: rootDir })
+  const app = createApp(nuxt)
+  await resolveApp(nuxt, app)
+
+  const normaliseToRepo = (id?: string | null) =>
+    id?.replace(rootDir, '<rootDir>').replace(repoRoot, '<repoRoot>').replace(/.*node_modules\//, '')
+
+  app.dir = normaliseToRepo(app.dir)!
+
+  const componentKeys = ['rootComponent', 'errorComponent', 'mainComponent'] as const
+  for (const _key of componentKeys) {
+    const key = _key as typeof componentKeys[number]
+    app[key] = normaliseToRepo(app[key])
+  }
+  for (const plugin of app.plugins) {
+    plugin.src = normaliseToRepo(plugin.src)!
+  }
+  for (const mw of app.middleware) {
+    mw.path = normaliseToRepo(mw.path)!
+  }
+
+  for (const layout in app.layouts) {
+    app.layouts[layout].file = normaliseToRepo(app.layouts[layout].file)!
+  }
+
+  await nuxt.close()
+
+  return app
+}