Use test fixtures

Author: ehmicky

package-lock.json

@@ -35,7 +35,6 @@
     "@netlify/eslint-config-node": "^0.3.0",
     "husky": "^4.3.0",
     "jest": "^26.6.1",
-    "mock-fs": "^4.13.0",
     "prettier": "^2.1.2",
     "react": "^17.0.1",
     "react-dom": "^17.0.1"
@@ -47,7 +46,8 @@
   },
   "jest": {
     "testMatch": [
-      "**/test/**/*.js"
+      "**/test/**/*.js",
+      "!**/test/fixtures/**"
     ],
     "verbose": true
   }

package.json

@@ -0,0 +1,3 @@
+module.exports = {
+  target: 'server',
+}

test/fixtures/invalid_next_config/next.config.js

@@ -1,9 +1,9 @@
 const path = require('path')
+const process = require('process')
 const nextOnNetlify = require('next-on-netlify')
 const makef = require('makef')
 const makeDir = require('make-dir')
 const cpx = require('cpx')
-const mockFs = require('mock-fs')
 const plugin = require('../index')
 
 const utils = {
@@ -33,6 +33,14 @@ console.log('Initializing tests')
 
 const DUMMY_PACKAGE_JSON = { name: 'dummy', version: '1.0.0' }
 
+const FIXTURES_DIR = `${__dirname}/fixtures`
+
+const useFixture = function (fixtureName) {
+  const originalCwd = process.cwd()
+  process.chdir(`${FIXTURES_DIR}/${fixtureName}`)
+  return process.chdir.bind(process, originalCwd)
+}
+
 describe('preBuild()', () => {
   test('fail build if the app has static html export in npm script', async () => {
     await plugin.onPreBuild({
@@ -98,11 +106,7 @@ describe('preBuild()', () => {
   })
 
   test(`fail build if the app's next config has an invalid target`, async () => {
-    mockFs({
-      'next.config.js': {
-        target: 'nonsense',
-      },
-    })
+    const restoreCwd = useFixture('invalid_next_config')
 
     await plugin.onPreBuild({
       netlifyConfig: {},
@@ -111,7 +115,7 @@ describe('preBuild()', () => {
       constants: { FUNCTIONS_SRC: 'out_functions' },
     })
 
-    mockFs.restore()
+    restoreCwd()
 
     const acceptableTargets = ['serverless', 'experimental-serverless-trace']
     expect(utils.build.failBuild.mock.calls[0][0]).toEqual(