added test for empty next.config file

test/integration/invalid-config-file/pages/index.js

@@ -0,0 +1 @@
+export default () => 'hi'

test/integration/invalid-config-file/test/index.test.js

@@ -0,0 +1,50 @@
+/* eslint-env jest */
+/* global jasmine */
+import fs from 'fs-extra'
+import { join } from 'path'
+import { nextBuild } from 'next-test-utils'
+
+const appDir = join(__dirname, '../')
+const nextConfigPath = join(appDir, 'next.config.js')
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 2
+
+const cleanUp = () => fs.remove(nextConfigPath)
+
+describe('Handles valid/invalid next.config.js', () => {
+  beforeAll(() => cleanUp())
+  afterAll(() => cleanUp())
+
+  it('should not error when config has an exported object', async () => {
+    await fs.writeFile(
+      nextConfigPath,
+      `module.exports = {
+      }`
+    )
+
+    const { stderr } = await nextBuild(appDir, undefined, { stderr: true })
+    expect(stderr).not.toMatch(
+      /`next.config.js` file found, but nothing was exported from it/
+    )
+  })
+
+  // it('should not error when config has an exported function', async () => {
+  //   await fs.writeFile(
+  //     nextConfigPath,
+  //     `module.exports = () => {
+  //       return {}
+  //     }`
+  //   )
+
+  //   const { stderr } = await nextBuild(appDir, undefined, { stderr: true })
+  //   expect(stderr).not.toMatch(/`next.config.js` file found, but nothing was exported from it/)
+  // })
+
+  it('should error when no export is defined', async () => {
+    await fs.writeFile(nextConfigPath, `{}`)
+
+    const { stderr } = await nextBuild(appDir, undefined, { stderr: true })
+    expect(stderr).toMatch(
+      /`next.config.js` file found, but nothing was exported from it/
+    )
+  })
+})