fix(make_it_modular): use proxyquire for mock fs

exercises/make_it_modular/verify.js

@@ -1,7 +1,7 @@
-const fs = require('fs')
 const path = require('path')
 const util = require('util')
 const files = require('../filtered_ls/file-list')
+const proxyquire = require('proxyquire')
 
 function validateModule (modFile, callback) {
   const exercise = this
@@ -48,20 +48,22 @@ function validateModule (modFile, callback) {
   exercise.emit('pass', __n('pass.arguments', mod.length))
 
   // ---- Mock `fs.readdir` and check that an error bubbles back up through the cb
-
-  fs.$readdir = fs.readdir
-  fs.readdir = function (dir, optionalEncoding, callback) {
-    callback = callback || optionalEncoding
-    callback(error)
-  }
+  const mockMod = proxyquire(modFile, {
+    fs: {
+      readdir: function (dir, optionalEncoding, callback) {
+        callback = callback || optionalEncoding
+        callback(error)
+      }
+    }
+  })
 
   function noerr () {
     return modFileError(__('fail.mod.missing_error'))
   }
 
   callbackUsed = false
   try {
-    mod('/foo/bar/', 'wheee', function (err) {
+    mockMod('/foo/bar/', 'wheee', function (err) {
       if (err !== error) {
         return noerr()
       }
@@ -89,9 +91,6 @@ function validateModule (modFile, callback) {
 
     exercise.emit('pass', __('pass.callback'))
 
-    // replace the mock readdir
-    fs.readdir = fs.$readdir
-
     callbackUsed = false
 
     // a special follow-up for when we detect they are not passing back

package.json

@@ -66,6 +66,7 @@
     "concat-stream": "^2.0.0",
     "duplexer": "^0.1.1",
     "hyperquest": "^2.1.3",
+    "proxyquire": "^2.1.3",
     "rimraf": "^3.0.0",
     "through2": "^3.0.1",
     "through2-map": "^3.0.0",

test/make_it_modular/module_valid_03.js

@@ -0,0 +1,13 @@
+const { readdir } = require('fs')
+const { extname } = require('path')
+
+module.exports = (directory, extension, callback) => {
+  const isExtension = (file) => extname(file) === `.${extension}`
+
+  readdir(directory, (err, files) => {
+    if (err) return callback(err)
+
+    const matchingFiles = files.filter(isExtension)
+    callback(null, matchingFiles)
+  })
+}

test/make_it_modular/valid_03.js

@@ -0,0 +1,9 @@
+const mod = require('./module_valid_03')
+
+mod(process.argv[2], process.argv[3], (error, list) => {
+  if (error) return console.log(error)
+
+  list.forEach((entry) => {
+    console.log(entry)
+  })
+})