Add dev test too

Author: devknoll

packages/next/next-server/server/render.tsx

@@ -460,7 +460,10 @@ export async function renderToHTML(
     !isSSG &&
     !getServerSideProps
 
-  if (process.env.NEXT_CONCURRENT_FEATURES && typeof Document !== 'function') {
+  if (
+    (process.env.NEXT_CONCURRENT_FEATURES && typeof Document !== 'function') ||
+    Document.prototype
+  ) {
     throw new Error(CUSTOM_DOCUMENT_RSC_ERROR + ` ${pathname}`)
   }
 

test/integration/concurrent-document-component-error/test/index.test.js

@@ -1,7 +1,13 @@
 /* eslint-env jest */
 
 import { join } from 'path'
-import { nextBuild } from 'next-test-utils'
+import {
+  renderViaHTTP,
+  findPort,
+  launchApp,
+  killApp,
+  nextBuild,
+} from 'next-test-utils'
 import { CUSTOM_DOCUMENT_RSC_ERROR } from 'next/dist/lib/constants'
 
 jest.setTimeout(1000 * 60)
@@ -12,4 +18,25 @@ describe('Concurrent Document Component Errors', () => {
     const { stderr } = await nextBuild(appDir, [], { stderr: true })
     expect(stderr).toContain(CUSTOM_DOCUMENT_RSC_ERROR)
   })
+
+  describe('development mode', () => {
+    let output
+
+    beforeAll(async () => {
+      const handleOutput = (msg) => {
+        output += msg
+      }
+      const appPort = await findPort()
+      const app = await launchApp(appDir, appPort, {
+        onStdout: handleOutput,
+        onStderr: handleOutput,
+      })
+      await renderViaHTTP(appPort, '/')
+      await killApp(app)
+    })
+
+    it('errors when document is a class component', () => {
+      expect(output).toContain(CUSTOM_DOCUMENT_RSC_ERROR)
+    })
+  })
 })