feat(test-utils): allow mounting single component for testing

packages/nuxt/src/app/components/nuxt-root.vue

@@ -2,6 +2,7 @@
   <Suspense @resolve="onResolve">
     <ErrorComponent v-if="error" :error="error" />
     <IslandRenderer v-else-if="islandContext" :context="islandContext" />
+    <component :is="SingleRenderer" v-else-if="SingleRenderer" />
     <AppComponent v-else />
   </Suspense>
 </template>
@@ -21,6 +22,10 @@ const IslandRenderer = process.server
 const nuxtApp = useNuxtApp()
 const onResolve = nuxtApp.deferHydration()
 
+const url = process.server ? nuxtApp.ssrContext.url : window.location.pathname
+const SingleRenderer = process.dev && process.server && url.startsWith('/__nuxt_component_test__/') && defineAsyncComponent(() => import('#build/test-component-wrapper.mjs')
+  .then(r => r.default(process.server ? url : window.location.href)))
+
 // Inject default route (outside of pages) as active route
 provide('_route', useRoute())
 

packages/nuxt/src/app/components/test-component-wrapper.ts

@@ -0,0 +1,19 @@
+import { parseURL } from 'ufo'
+import { defineComponent, h } from 'vue'
+import { parseQuery } from 'vue-router'
+
+export default (url:string) => defineComponent({
+  name: 'NuxtTestComponentWrapper',
+
+  async setup (props, { attrs }) {
+    const query = parseQuery(parseURL(url).search)
+    const urlProps = query.props ? JSON.parse(query.props as string) : {}
+    const comp = await import(/* @vite-ignore */ query.path as string).then(r => r.default)
+    return () => [
+      h('div', 'Component Test Wrapper for ' + query.path),
+      h('div', { id: 'nuxt-component-root' }, [
+        h(comp, { ...attrs, ...props, ...urlProps })
+      ])
+    ]
+  }
+})

packages/nuxt/src/core/templates.ts

@@ -40,6 +40,11 @@ export const errorComponentTemplate: NuxtTemplate<TemplateContext> = {
   filename: 'error-component.mjs',
   getContents: ctx => genExport(ctx.app.errorComponent!, ['default'])
 }
+// TODO: Use an alias
+export const testComponentWrapperTemplate = {
+  filename: 'test-component-wrapper.mjs',
+  getContents: (ctx: TemplateContext) => genExport(resolve(ctx.nuxt.options.appDir, 'components/test-component-wrapper'), ['default'])
+}
 
 export const cssTemplate: NuxtTemplate<TemplateContext> = {
   filename: 'css.mjs',

packages/test-utils/build.config.ts

@@ -4,6 +4,7 @@ export default defineBuildConfig({
   declaration: true,
   entries: [
     'src/index',
+    'src/experimental',
     { input: 'src/runtime/', outDir: 'dist/runtime', format: 'esm' }
   ],
   externals: [

packages/test-utils/experimental.d.ts

@@ -0,0 +1 @@
+export * from './dist/experimental'

packages/test-utils/package.json

@@ -9,6 +9,10 @@
     ".": {
       "types": "./dist/index.d.ts",
       "import": "./dist/index.mjs"
+    },
+    "./experimental": {
+      "types": "./dist/experimental.d.ts",
+      "import": "./dist/experimental.mjs"
     }
   },
   "files": [
@@ -26,7 +30,8 @@
     "get-port-please": "^3.0.1",
     "jiti": "^1.18.2",
     "ofetch": "^1.0.1",
-    "pathe": "^1.1.0"
+    "pathe": "^1.1.0",
+    "ufo": "^1.1.1"
   },
   "devDependencies": {
     "playwright": "^1.32.2",

packages/test-utils/src/experimental.ts

@@ -0,0 +1,23 @@
+import { fetch as _fetch, $fetch as _$fetch } from 'ofetch'
+import * as _kit from '@nuxt/kit'
+import { resolve } from 'pathe'
+import { stringifyQuery } from 'ufo'
+import { useTestContext } from './context'
+import { $fetch } from './server'
+
+/**
+ * This is a function to render a component directly with the Nuxt server.
+ */
+export function $fetchComponent (filepath: string, props?: Record<string, any>) {
+  return $fetch(componentTestUrl(filepath, props))
+}
+
+export function componentTestUrl (filepath: string, props?: Record<string, any>) {
+  const ctx = useTestContext()
+  filepath = resolve(ctx.options.rootDir, filepath)
+  const path = stringifyQuery({
+    path: filepath,
+    props: JSON.stringify(props)
+  })
+  return `/__nuxt_component_test__/?${path}`
+}

packages/test-utils/src/server.ts

@@ -1,9 +1,9 @@
-import { resolve } from 'node:path'
 import { execa } from 'execa'
 import { getRandomPort, waitForPort } from 'get-port-please'
 import type { FetchOptions } from 'ofetch'
 import { fetch as _fetch, $fetch as _$fetch } from 'ofetch'
 import * as _kit from '@nuxt/kit'
+import { resolve } from 'pathe'
 import { useTestContext } from './context'
 
 // @ts-ignore type cast
@@ -75,5 +75,8 @@ export function url (path: string) {
   if (!ctx.url) {
     throw new Error('url is not available (is server option enabled?)')
   }
+  if (path.startsWith(ctx.url)) {
+    return path
+  }
   return ctx.url + path
 }

test/basic.test.ts

@@ -7,6 +7,7 @@ import { setup, fetch, $fetch, startServer, isDev, createPage, url } from '@nuxt
 
 import type { NuxtIslandResponse } from '../packages/nuxt/src/core/runtime/nitro/renderer'
 import { expectNoClientErrors, expectWithPolling, renderPage, withLogs } from './utils'
+import { $fetchComponent } from '@nuxt/test-utils/experimental'
 
 const isWebpack = process.env.TEST_BUILDER === 'webpack'
 
@@ -1277,3 +1278,13 @@ describe.skipIf(isWindows)('useAsyncData', () => {
     await expectNoClientErrors('/useAsyncData/promise-all')
   })
 })
+
+describe.runIf(isDev())('component testing', () => {
+  it('should work', async () => {
+    const comp1 = await $fetchComponent('components/SugarCounter.vue', { multiplier: 2 })
+    expect(comp1).toContain('12 x 2 = 24')
+
+    const comp2 = await $fetchComponent('components/SugarCounter.vue', { multiplier: 4 })
+    expect(comp2).toContain('12 x 4 = 48')
+  })
+})

vitest.config.ts

@@ -7,6 +7,7 @@ export default defineConfig({
   resolve: {
     alias: {
       '#app': resolve('./packages/nuxt/dist/app/index'),
+      '@nuxt/test-utils/experimental': resolve('./packages/test-utils/src/experimental.ts'),
       '@nuxt/test-utils': resolve('./packages/test-utils/src/index.ts')
     }
   },