Add integration test to cover vercel#7894

test/integration/build-firebase-only-sequentially/pages/page-1.js

@@ -0,0 +1,2 @@
+import 'firebase/firestore'
+export default () => <div>Firebase</div>

test/integration/build-firebase-only-sequentially/pages/page-2.js

@@ -0,0 +1,2 @@
+import 'firebase/firestore'
+export default () => <div>Firebase</div>

test/integration/build-firebase-only-sequentially/test/index.test.js

@@ -0,0 +1,37 @@
+/* eslint-env jest */
+/* global jasmine */
+import path from 'path'
+import fs from 'fs-extra'
+import { nextBuild } from 'next-test-utils'
+
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 1
+const appDir = path.join(__dirname, '..')
+const nextConfig = path.join(appDir, 'next.config.js')
+
+describe('Builds with firebase dependency only sequentially', () => {
+  it('Throws an error when building with firebase dependency in parallel', async () => {
+    await fs.writeFile(
+      nextConfig,
+      `module.exports = { experimental: { cpus: 2 } }`
+    )
+    const results = await nextBuild(appDir, [], { stdout: true, stderr: true })
+    expect(results.stdout + results.stderr).toMatch(/Build error occurred/)
+    expect(results.stdout + results.stderr).toMatch(
+      /grpc_node\.node\. Module did not self-register\./
+    )
+    await fs.remove(nextConfig)
+  })
+
+  it('Throws no error when building with firebase dependency in sequence', async () => {
+    await fs.writeFile(
+      nextConfig,
+      `module.exports = { experimental: { cpus: 1 } }`
+    )
+    const results = await nextBuild(appDir, [], { stdout: true, stderr: true })
+    expect(results.stdout + results.stderr).not.toMatch(/Build error occurred/)
+    expect(results.stdout + results.stderr).not.toMatch(
+      /grpc_node\.node\. Module did not self-register\./
+    )
+    await fs.remove(nextConfig)
+  })
+})