diff --git a/tracker/test/attachment_helpers_test.py b/tracker/test/attachment_helpers_test.py
new file mode 100644
index 0000000..18e0efc
--- /dev/null
+++ b/tracker/test/attachment_helpers_test.py
@@ -0,0 +1,149 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+"""Unittest for the tracker helpers module."""
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+
+from mock import Mock, patch
+import unittest
+
+from proto import tracker_pb2
+from tracker import attachment_helpers
+
+
+class AttachmentHelpersFunctionsTest(unittest.TestCase):
+
+  def testIsViewableImage(self):
+    self.assertTrue(attachment_helpers.IsViewableImage('image/gif', 123))
+    self.assertTrue(attachment_helpers.IsViewableImage(
+        'image/gif; charset=binary', 123))
+    self.assertTrue(attachment_helpers.IsViewableImage('image/png', 123))
+    self.assertTrue(attachment_helpers.IsViewableImage(
+        'image/png; charset=binary', 123))
+    self.assertTrue(attachment_helpers.IsViewableImage('image/x-png', 123))
+    self.assertTrue(attachment_helpers.IsViewableImage('image/jpeg', 123))
+    self.assertTrue(attachment_helpers.IsViewableImage(
+        'image/jpeg; charset=binary', 123))
+    self.assertTrue(attachment_helpers.IsViewableImage(
+        'image/jpeg', 14 * 1024 * 1024))
+
+    self.assertFalse(attachment_helpers.IsViewableImage('junk/bits', 123))
+    self.assertFalse(attachment_helpers.IsViewableImage(
+        'junk/bits; charset=binary', 123))
+    self.assertFalse(attachment_helpers.IsViewableImage(
+        'image/jpeg', 16 * 1024 * 1024))
+
+  def testIsViewableVideo(self):
+    self.assertTrue(attachment_helpers.IsViewableVideo('video/ogg', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo(
+        'video/ogg; charset=binary', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo('video/mp4', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo(
+        'video/mp4; charset=binary', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo('video/mpg', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo(
+        'video/mpg; charset=binary', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo('video/mpeg', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo(
+        'video/mpeg; charset=binary', 123))
+    self.assertTrue(attachment_helpers.IsViewableVideo(
+        'video/mpeg', 14 * 1024 * 1024))
+
+    self.assertFalse(attachment_helpers.IsViewableVideo('junk/bits', 123))
+    self.assertFalse(attachment_helpers.IsViewableVideo(
+        'junk/bits; charset=binary', 123))
+    self.assertFalse(attachment_helpers.IsViewableVideo(
+        'video/mp4', 16 * 1024 * 1024))
+
+  def testIsViewableText(self):
+    self.assertTrue(attachment_helpers.IsViewableText('text/plain', 0))
+    self.assertTrue(attachment_helpers.IsViewableText('text/plain', 1000))
+    self.assertTrue(attachment_helpers.IsViewableText('text/html', 1000))
+    self.assertFalse(
+        attachment_helpers.IsViewableText('text/plain', 200 * 1024 * 1024))
+    self.assertFalse(attachment_helpers.IsViewableText('image/jpeg', 200))
+    self.assertFalse(
+        attachment_helpers.IsViewableText('image/jpeg', 200 * 1024 * 1024))
+
+  def testSignAttachmentID(self):
+    pass  # TODO(jrobbins): write tests
+
+  @patch('tracker.attachment_helpers.SignAttachmentID')
+  def testGetDownloadURL(self, mock_SignAttachmentID):
+    """The download URL is always our to attachment servlet."""
+    mock_SignAttachmentID.return_value = 67890
+    self.assertEqual(
+      'attachment?aid=12345&signed_aid=67890',
+      attachment_helpers.GetDownloadURL(12345))
+
+  def testGetViewURL(self):
+    """The view URL may add &inline=1, or use our text attachment servlet."""
+    attach = tracker_pb2.Attachment(
+        attachment_id=1, mimetype='see below', filesize=1000)
+    download_url = 'attachment?aid=1&signed_aid=2'
+
+    # Viewable image.
+    attach.mimetype = 'image/jpeg'
+    self.assertEqual(
+      download_url + '&inline=1',
+      attachment_helpers.GetViewURL(attach, download_url, 'proj'))
+
+    # Viewable video.
+    attach.mimetype = 'video/mpeg'
+    self.assertEqual(
+      download_url + '&inline=1',
+      attachment_helpers.GetViewURL(attach, download_url, 'proj'))
+
+    # Viewable text file.
+    attach.mimetype = 'text/html'
+    self.assertEqual(
+      '/p/proj/issues/attachmentText?aid=1',
+      attachment_helpers.GetViewURL(attach, download_url, 'proj'))
+
+    # Something we don't support.
+    attach.mimetype = 'audio/mp3'
+    self.assertIsNone(
+      attachment_helpers.GetViewURL(attach, download_url, 'proj'))
+
+  def testGetThumbnailURL(self):
+    """The thumbnail URL may add param thumb=1 or not."""
+    attach = tracker_pb2.Attachment(
+        attachment_id=1, mimetype='see below', filesize=1000)
+    download_url = 'attachment?aid=1&signed_aid=2'
+
+    # Viewable image.
+    attach.mimetype = 'image/jpeg'
+    self.assertEqual(
+      download_url + '&inline=1&thumb=1',
+      attachment_helpers.GetThumbnailURL(attach, download_url))
+
+    # Viewable video.
+    attach.mimetype = 'video/mpeg'
+    self.assertIsNone(
+      # Video thumbs are displayed via GetVideoURL rather than this.
+      attachment_helpers.GetThumbnailURL(attach, download_url))
+
+    # Something that we don't thumbnail.
+    attach.mimetype = 'audio/mp3'
+    self.assertIsNone(attachment_helpers.GetThumbnailURL(attach, download_url))
+
+  def testGetVideoURL(self):
+    """The video URL is the same as the view URL for actual videos."""
+    attach = tracker_pb2.Attachment(
+        attachment_id=1, mimetype='see below', filesize=1000)
+    download_url = 'attachment?aid=1&signed_aid=2'
+
+    # Viewable video.
+    attach.mimetype = 'video/mpeg'
+    self.assertEqual(
+      download_url + '&inline=1',
+      attachment_helpers.GetVideoURL(attach, download_url))
+
+    # Anything that is not a video.
+    attach.mimetype = 'audio/mp3'
+    self.assertIsNone(attachment_helpers.GetVideoURL(attach, download_url))
+