diff --git a/external/builder/fixtures_esprima/comments-expected.js b/external/builder/fixtures_esprima/comments-expected.js
index f36ff416d..f216553cb 100644
--- a/external/builder/fixtures_esprima/comments-expected.js
+++ b/external/builder/fixtures_esprima/comments-expected.js
@@ -1,28 +1,17 @@
 function f1() {
- /* head */
  "1";
- /* mid */
  "2";
 }
-/* tail */
 function f2() {
- // head
  "1";
- // mid
  "2";
 }
-// tail
 function f2() {
  if ("1") {
-  // begin block
   "1";
  }
  "2";
- // trailing
- if (/* s */
-  "3")
-  /*e*/
-  {
-   "4";
-  }
+ if ("3") {
+  "4";
+ }
 }
diff --git a/external/builder/test-fixtures.js b/external/builder/test-fixtures.js
index 12fc8af89..17d52a784 100644
--- a/external/builder/test-fixtures.js
+++ b/external/builder/test-fixtures.js
@@ -1,17 +1,20 @@
 'use strict';
 
-require('shelljs/make');
-
 var builder = require('./builder');
 var fs = require('fs');
+var path = require('path');
 
 var errors = 0;
 
-cd(__dirname);
-cd('fixtures');
-ls('*-expected.*').forEach(function(expectationFilename) {
+var baseDir = path.join(__dirname, 'fixtures');
+var files = fs.readdirSync(baseDir).filter(function (name) {
+  return /-expected\./.test(name);
+}).map(function (name) {
+  return path.join(baseDir, name);
+});
+files.forEach(function(expectationFilename) {
   var inFilename = expectationFilename.replace('-expected', '');
-  var expectation = cat(expectationFilename).trim()
+  var expectation = fs.readFileSync(expectationFilename).toString().trim()
     .replace(/__filename/g, fs.realpathSync(inFilename));
   var outLines = [];
 
@@ -32,20 +35,22 @@ ls('*-expected.*').forEach(function(expectationFilename) {
   if (out !== expectation) {
     errors++;
 
-    echo('Assertion failed for ' + inFilename);
-    echo('--------------------------------------------------');
-    echo('EXPECTED:');
-    echo(expectation);
-    echo('--------------------------------------------------');
-    echo('ACTUAL');
-    echo(out);
-    echo('--------------------------------------------------');
-    echo();
+    console.log('Assertion failed for ' + inFilename);
+    console.log('--------------------------------------------------');
+    console.log('EXPECTED:');
+    console.log(expectation);
+    console.log('--------------------------------------------------');
+    console.log('ACTUAL');
+    console.log(out);
+    console.log('--------------------------------------------------');
+    console.log();
   }
 });
 
 if (errors) {
-  echo('Found ' + errors + ' expectation failures.');
+  console.error('Found ' + errors + ' expectation failures.');
+  process.exit(1);
 } else {
-  echo('All tests completed without errors.');
+  console.log('All tests completed without errors.');
+  process.exit(0);
 }
diff --git a/external/builder/test-fixtures_esprima.js b/external/builder/test-fixtures_esprima.js
index 108d9a35a..944e91a04 100644
--- a/external/builder/test-fixtures_esprima.js
+++ b/external/builder/test-fixtures_esprima.js
@@ -1,17 +1,20 @@
 'use strict';
 
-require('shelljs/make');
-
 var p2 = require('./preprocessor2.js');
 var fs = require('fs');
+var path = require('path');
 
 var errors = 0;
 
-cd(__dirname);
-cd('fixtures_esprima');
-ls('*-expected.*').forEach(function(expectationFilename) {
+var baseDir = path.join(__dirname, 'fixtures_esprima');
+var files = fs.readdirSync(baseDir).filter(function (name) {
+  return /-expected\./.test(name);
+}).map(function (name) {
+  return path.join(baseDir, name);
+});
+files.forEach(function(expectationFilename) {
   var inFilename = expectationFilename.replace('-expected', '');
-  var expectation = cat(expectationFilename).trim()
+  var expectation = fs.readFileSync(expectationFilename).toString().trim()
     .replace(/__filename/g, fs.realpathSync(inFilename));
   var input = fs.readFileSync(inFilename).toString();
 
@@ -24,7 +27,6 @@ ls('*-expected.*').forEach(function(expectationFilename) {
   var ctx = {
     defines: defines,
     rootPath: __dirname + '/../..',
-    saveComments: true
   };
   var out;
   try {
@@ -35,20 +37,22 @@ ls('*-expected.*').forEach(function(expectationFilename) {
   if (out !== expectation) {
     errors++;
 
-    echo('Assertion failed for ' + inFilename);
-    echo('--------------------------------------------------');
-    echo('EXPECTED:');
-    echo(expectation);
-    echo('--------------------------------------------------');
-    echo('ACTUAL');
-    echo(out);
-    echo('--------------------------------------------------');
-    echo();
+    console.log('Assertion failed for ' + inFilename);
+    console.log('--------------------------------------------------');
+    console.log('EXPECTED:');
+    console.log(expectation);
+    console.log('--------------------------------------------------');
+    console.log('ACTUAL');
+    console.log(out);
+    console.log('--------------------------------------------------');
+    console.log();
   }
 });
 
 if (errors) {
-  echo('Found ' + errors + ' expectation failures.');
+  console.error('Found ' + errors + ' expectation failures.');
+  process.exit(1);
 } else {
-  echo('All tests completed without errors.');
+  console.log('All tests completed without errors.');
+  process.exit(0);
 }
diff --git a/gulpfile.js b/gulpfile.js
index 703981b9c..9371002e0 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -1424,3 +1424,12 @@ gulp.task('mozcentraldiff', ['mozcentral', 'mozcentralbaseline'],
           });
       });
 });
+
+gulp.task('externaltest', function () {
+  gutil.log('Running test-fixtures.js');
+  safeSpawnSync('node', ['external/builder/test-fixtures.js'],
+                {stdio: 'inherit'});
+  gutil.log('Running test-fixtures_esprima.js');
+  safeSpawnSync('node', ['external/builder/test-fixtures_esprima.js'],
+                {stdio: 'inherit'});
+});
diff --git a/package.json b/package.json
index 982a7e148..e3ee2c866 100644
--- a/package.json
+++ b/package.json
@@ -35,7 +35,7 @@
     "yargs": "^3.14.0"
   },
   "scripts": {
-    "test": "gulp lint unittestcli"
+    "test": "gulp lint unittestcli externaltest"
   },
   "repository": {
     "type": "git",