--- a/taskcluster/taskgraph/test/test_util_docker.py
+++ b/taskcluster/taskgraph/test/test_util_docker.py
@@ -1,23 +1,28 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 from __future__ import absolute_import, print_function, unicode_literals
 
 import os
 import shutil
+import stat
+import tarfile
 import tempfile
 import unittest
 
 from ..util import docker
 from mozunit import MockedOpen
 
 
+MODE_STANDARD = stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP | stat.S_IROTH
+
+
 class TestDocker(unittest.TestCase):
 
     def test_generate_context_hash(self):
         tmpdir = tempfile.mkdtemp()
         old_GECKO = docker.GECKO
         docker.GECKO = tmpdir
         try:
             os.makedirs(os.path.join(tmpdir, 'docker', 'my-image'))
@@ -41,8 +46,34 @@ class TestDocker(unittest.TestCase):
             self.assertEqual(docker.docker_image('myimage'), "cool-images/myimage:1.2.3")
 
     def test_docker_image_default_registry(self):
         files = {}
         files["{}/REGISTRY".format(docker.DOCKER_ROOT)] = "mozilla"
         files["{}/myimage/VERSION".format(docker.DOCKER_ROOT)] = "1.2.3"
         with MockedOpen(files):
             self.assertEqual(docker.docker_image('myimage'), "mozilla/myimage:1.2.3")
+
+    def test_create_context_tar_basic(self):
+        tmp = tempfile.mkdtemp()
+        try:
+            d = os.path.join(tmp, 'test_image')
+            os.mkdir(d)
+            with open(os.path.join(d, 'Dockerfile'), 'a'):
+                pass
+            os.chmod(os.path.join(d, 'Dockerfile'), MODE_STANDARD)
+
+            with open(os.path.join(d, 'extra'), 'a'):
+                pass
+            os.chmod(os.path.join(d, 'extra'), MODE_STANDARD)
+
+            tp = os.path.join(tmp, 'tar')
+            h = docker.create_context_tar(tmp, d, tp, 'my_image')
+            self.assertEqual(h, '2a6d7f1627eba60daf85402418e041d728827d309143c6bc1c6bb3035bde6717')
+
+            # File prefix should be "my_image"
+            with tarfile.open(tp, 'r:gz') as tf:
+                self.assertEqual(tf.getnames(), [
+                    'my_image/Dockerfile',
+                    'my_image/extra',
+                ])
+        finally:
+            shutil.rmtree(tmp)