diff --git a/.gitignore b/.gitignore
index efe387af34..975bff0f78 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,7 @@ npm-debug.log
 .DS_Store
 hass_frontend/*
 hass_frontend_es5/*
+.reify-cache
 
 # Python stuff
 *.py[cod]
diff --git a/gulp/tasks/rollup.js b/gulp/tasks/rollup.js
index 57cd455972..a36816751e 100644
--- a/gulp/tasks/rollup.js
+++ b/gulp/tasks/rollup.js
@@ -6,6 +6,7 @@ const rollupConfigEs6 = require('../../rollup.config-es6');
 gulp.task('run_rollup_es5', () => gulp.src([
   'js/core.js',
   'js/compatibility.js',
+  'js/util.js',
   'js/automation-editor/automation-editor.js',
   'js/script-editor/script-editor.js',
   'demo_data/demo_data.js',
@@ -16,6 +17,7 @@ gulp.task('run_rollup_es5', () => gulp.src([
 gulp.task('run_rollup', () => gulp.src([
   'js/core.js',
   'js/automation-editor/automation-editor.js',
+  'js/util.js',
   'js/script-editor/script-editor.js',
   'demo_data/demo_data.js',
 ])
diff --git a/js/common/util/attribute_class_names.js b/js/common/util/attribute_class_names.js
new file mode 100644
index 0000000000..004e5bb0da
--- /dev/null
+++ b/js/common/util/attribute_class_names.js
@@ -0,0 +1,6 @@
+export default function attributeClassNames(stateObj, attributes) {
+  if (!stateObj) return '';
+  return attributes.map(function (attribute) {
+    return attribute in stateObj.attributes ? 'has-' + attribute : '';
+  }).filter(attr => attr !== '').join(' ');
+}
diff --git a/js/util.js b/js/util.js
new file mode 100644
index 0000000000..621f7e0019
--- /dev/null
+++ b/js/util.js
@@ -0,0 +1,13 @@
+/**
+ * Export hass util functions to window.
+ *
+ * This file is a workaround for the fact that Polymer 2 doesn't work well with
+ * ES6 JS imports. Once we move to Polymer 3, we should be able to simply
+ * import these functions where we need them.
+ */
+
+import attributeClassNames from './common/util/attribute_class_names';
+
+window.hassUtil = window.hassUtil || {};
+
+window.hassUtil.attributeClassNames = attributeClassNames;
diff --git a/package.json b/package.json
index befb354703..eee3d19151 100644
--- a/package.json
+++ b/package.json
@@ -17,7 +17,8 @@
     "dev-watch-es5": "npm run gulp watch_ru_all_es5 gen-service-worker-es5",
     "lint_js": "eslint src panels js --ext js,html",
     "lint_html": "ls -1 src/home-assistant.html panels/**/ha-panel-*.html | xargs polymer lint --input",
-    "test": "npm run lint_js && npm run lint_html"
+    "mocha": "node_modules/.bin/mocha --opts test-mocha/mocha.opts",
+    "test": "npm run lint_js && npm run lint_html && npm run mocha"
   },
   "author": "Paulus Schoutsen <Paulus@PaulusSchoutsen.nl> (http://paulusschoutsen.nl)",
   "license": "Apache-2.0",
@@ -58,6 +59,7 @@
     "home-assistant-js-websocket": "^1.1.2",
     "html-minifier": "^3.5.6",
     "merge-stream": "^1.0.1",
+    "mocha": "^4.0.1",
     "parse5": "^3.0.3",
     "polymer-analyzer": "^2.3.0",
     "polymer-build": "^2.1.0",
@@ -65,6 +67,7 @@
     "polymer-cli": "^1.5.6",
     "preact": "^8.2.6",
     "pump": "^1.0.2",
+    "reify": "^0.12.3",
     "require-dir": "^0.3.2",
     "rollup": "^0.51.3",
     "rollup-plugin-babel": "^3.0.2",
diff --git a/src/util/hass-util.html b/src/util/hass-util.html
index a1b9be3efe..3cf8d46c10 100644
--- a/src/util/hass-util.html
+++ b/src/util/hass-util.html
@@ -1,4 +1,5 @@
 <script src='../../bower_components/fecha/fecha.min.js'></script>
+<script src='../../build-temp/util.js'></script>
 
 <!--
 collection of utility functions.
@@ -38,13 +39,6 @@ window.hassUtil.HIDE_MORE_INFO = [
 window.hassUtil.LANGUAGE = navigator.languages ?
   navigator.languages[0] : navigator.language || navigator.userLanguage;
 
-window.hassUtil.attributeClassNames = function (stateObj, attributes) {
-  if (!stateObj) return '';
-  return attributes.map(function (attribute) {
-    return attribute in stateObj.attributes ? 'has-' + attribute : '';
-  }).join(' ');
-};
-
 // Expects featureClassNames to be an object mapping feature-bit -> className
 window.hassUtil.featureClassNames = function (stateObj, featureClassNames) {
   if (!stateObj || !stateObj.attributes.supported_features) return '';
diff --git a/test-mocha/common/util/attribute_class_names_test.js b/test-mocha/common/util/attribute_class_names_test.js
new file mode 100644
index 0000000000..fdd31c5983
--- /dev/null
+++ b/test-mocha/common/util/attribute_class_names_test.js
@@ -0,0 +1,53 @@
+import attributeClassNames from '../../../js/common/util/attribute_class_names';
+
+const assert = require('assert');
+
+describe('attributeClassNames', function() {
+  const attrs = ['mock_attr1', 'mock_attr2'];
+
+  it('null state', function() {
+    const stateObj = null;
+    assert.strictEqual(
+      attributeClassNames(stateObj, attrs),
+      '');
+  });
+
+  it('matches no attrbutes', function() {
+    const stateObj = {
+      attributes: {
+        other_attr_1: 1,
+        other_attr_2: 2,
+      },
+    };
+    assert.strictEqual(
+      attributeClassNames(stateObj, attrs),
+      '');
+  });
+
+  it('matches one attrbute', function() {
+    const stateObj = {
+      attributes: {
+        other_attr_1: 1,
+        other_attr_2: 2,
+        mock_attr1: 3,
+      },
+    };
+    assert.strictEqual(
+      attributeClassNames(stateObj, attrs),
+      'has-mock_attr1');
+  });
+
+  it('matches two attrbutes', function() {
+    const stateObj = {
+      attributes: {
+        other_attr_1: 1,
+        other_attr_2: 2,
+        mock_attr1: 3,
+        mock_attr2: null,
+      },
+    };
+    assert.strictEqual(
+      attributeClassNames(stateObj, attrs),
+      'has-mock_attr1 has-mock_attr2');
+  });
+});
diff --git a/test-mocha/mocha.opts b/test-mocha/mocha.opts
new file mode 100644
index 0000000000..59a615cb67
--- /dev/null
+++ b/test-mocha/mocha.opts
@@ -0,0 +1,5 @@
+-r reify
+--recursive
+--compilers js:babel-core/register
+--timeout 10000
+test-mocha
diff --git a/yarn.lock b/yarn.lock
index c0780ed7aa..914d1ba26a 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -500,6 +500,10 @@ acorn@^5.2.1:
   version "5.2.1"
   resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.2.1.tgz#317ac7821826c22c702d66189ab8359675f135d7"
 
+acorn@~5.1.1:
+  version "5.1.2"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.1.2.tgz#911cb53e036807cf0fa778dc5d370fbd864246d7"
+
 adm-zip@~0.4.3:
   version "0.4.7"
   resolved "https://registry.yarnpkg.com/adm-zip/-/adm-zip-0.4.7.tgz#8606c2cbf1c426ce8c8ec00174447fd49b6eafc1"
@@ -1957,7 +1961,7 @@ command-line-usage@^3.0.1, command-line-usage@^3.0.3, command-line-usage@^3.0.5:
     table-layout "^0.3.0"
     typical "^2.6.0"
 
-commander@2.11.x, commander@^2.9.0, commander@~2.11.0:
+commander@2.11.0, commander@2.11.x, commander@^2.9.0, commander@~2.11.0:
   version "2.11.0"
   resolved "https://registry.yarnpkg.com/commander/-/commander-2.11.0.tgz#157152fd1e7a6c8d98a5b715cf376df928004563"
 
@@ -2243,7 +2247,7 @@ debug@2.6.8, debug@^2.2.0, debug@^2.6.8:
   dependencies:
     ms "2.0.0"
 
-debug@^3.0.1:
+debug@3.1.0, debug@^3.0.1:
   version "3.1.0"
   resolved "https://registry.yarnpkg.com/debug/-/debug-3.1.0.tgz#5bb5a0672628b64149566ba16819e61518c67261"
   dependencies:
@@ -2378,6 +2382,10 @@ diff@3.2.0:
   version "3.2.0"
   resolved "https://registry.yarnpkg.com/diff/-/diff-3.2.0.tgz#c9ce393a4b7cbd0b058a725c93df299027868ff9"
 
+diff@3.3.1:
+  version "3.3.1"
+  resolved "https://registry.yarnpkg.com/diff/-/diff-3.3.1.tgz#aa8567a6eed03c531fc89d3f711cd0e5259dec75"
+
 diff@^2.1.2:
   version "2.2.3"
   resolved "https://registry.yarnpkg.com/diff/-/diff-2.2.3.tgz#60eafd0d28ee906e4e8ff0a52c1229521033bf99"
@@ -3457,6 +3465,17 @@ glob@7.1.1:
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
+glob@7.1.2, glob@^7.0.0, glob@^7.0.3, glob@^7.0.5, glob@^7.1.1, glob@^7.1.2:
+  version "7.1.2"
+  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.2.tgz#c19c9df9a028702d678612384a6552404c636d15"
+  dependencies:
+    fs.realpath "^1.0.0"
+    inflight "^1.0.4"
+    inherits "2"
+    minimatch "^3.0.4"
+    once "^1.3.0"
+    path-is-absolute "^1.0.0"
+
 glob@^4.3.1:
   version "4.5.3"
   resolved "https://registry.yarnpkg.com/glob/-/glob-4.5.3.tgz#c6cb73d3226c1efef04de3c56d012f03377ee15f"
@@ -3486,17 +3505,6 @@ glob@^6.0.1:
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
-glob@^7.0.0, glob@^7.0.3, glob@^7.0.5, glob@^7.1.1, glob@^7.1.2:
-  version "7.1.2"
-  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.2.tgz#c19c9df9a028702d678612384a6552404c636d15"
-  dependencies:
-    fs.realpath "^1.0.0"
-    inflight "^1.0.4"
-    inherits "2"
-    minimatch "^3.0.4"
-    once "^1.3.0"
-    path-is-absolute "^1.0.0"
-
 glob@~3.1.21:
   version "3.1.21"
   resolved "https://registry.yarnpkg.com/glob/-/glob-3.1.21.tgz#d29e0a055dea5138f4d07ed40e8982e83c2066cd"
@@ -3644,6 +3652,10 @@ grouped-queue@^0.3.0:
   dependencies:
     lodash "^4.17.2"
 
+growl@1.10.3:
+  version "1.10.3"
+  resolved "https://registry.yarnpkg.com/growl/-/growl-1.10.3.tgz#1926ba90cf3edfe2adb4927f5880bc22c66c790f"
+
 growl@1.9.2:
   version "1.9.2"
   resolved "https://registry.yarnpkg.com/growl/-/growl-1.9.2.tgz#0ea7743715db8d8de2c5ede1775e1b45ac85c02f"
@@ -5344,6 +5356,18 @@ minimist@^1.1.0, minimist@^1.1.3, minimist@^1.2.0:
   version "1.2.0"
   resolved "https://registry.yarnpkg.com/minimist/-/minimist-1.2.0.tgz#a35008b20f41383eec1fb914f4cd5df79a264284"
 
+minipass@^2.2.1:
+  version "2.2.1"
+  resolved "https://registry.yarnpkg.com/minipass/-/minipass-2.2.1.tgz#5ada97538b1027b4cf7213432428578cb564011f"
+  dependencies:
+    yallist "^3.0.0"
+
+minizlib@^1.0.3:
+  version "1.0.4"
+  resolved "https://registry.yarnpkg.com/minizlib/-/minizlib-1.0.4.tgz#8ebb51dd8bbe40b0126b5633dbb36b284a2f523c"
+  dependencies:
+    minipass "^2.2.1"
+
 mkdirp@0.5.0:
   version "0.5.0"
   resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.5.0.tgz#1d73076a6df986cd9344e15e71fcc05a4c9abf12"
@@ -5373,6 +5397,21 @@ mocha@^3.4.2:
     mkdirp "0.5.1"
     supports-color "3.1.2"
 
+mocha@^4.0.1:
+  version "4.0.1"
+  resolved "https://registry.yarnpkg.com/mocha/-/mocha-4.0.1.tgz#0aee5a95cf69a4618820f5e51fa31717117daf1b"
+  dependencies:
+    browser-stdout "1.3.0"
+    commander "2.11.0"
+    debug "3.1.0"
+    diff "3.3.1"
+    escape-string-regexp "1.0.5"
+    glob "7.1.2"
+    growl "1.10.3"
+    he "1.1.1"
+    mkdirp "0.5.1"
+    supports-color "4.4.0"
+
 ms@0.7.0:
   version "0.7.0"
   resolved "https://registry.yarnpkg.com/ms/-/ms-0.7.0.tgz#865be94c2e7397ad8a57da6a633a6e2f30798b83"
@@ -6533,6 +6572,14 @@ regjsparser@^0.1.4:
   dependencies:
     jsesc "~0.5.0"
 
+reify@^0.12.3:
+  version "0.12.3"
+  resolved "https://registry.yarnpkg.com/reify/-/reify-0.12.3.tgz#b1aa0c196e7dc7fb7e9ad42b87c1e10fe7f97f97"
+  dependencies:
+    acorn "~5.1.1"
+    minizlib "^1.0.3"
+    semver "^5.3.0"
+
 relateurl@0.2.x:
   version "0.2.7"
   resolved "https://registry.yarnpkg.com/relateurl/-/relateurl-0.2.7.tgz#54dbf377e51440aca90a4cd274600d3ff2d888a9"
@@ -7434,6 +7481,12 @@ supports-color@3.1.2:
   dependencies:
     has-flag "^1.0.0"
 
+supports-color@4.4.0, supports-color@^4.0.0:
+  version "4.4.0"
+  resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-4.4.0.tgz#883f7ddabc165142b2a61427f3352ded195d1a3e"
+  dependencies:
+    has-flag "^2.0.0"
+
 supports-color@^0.2.0:
   version "0.2.0"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-0.2.0.tgz#d92de2694eb3f67323973d7ae3d8b55b4c22190a"
@@ -7442,12 +7495,6 @@ supports-color@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-2.0.0.tgz#535d045ce6b6363fa40117084629995e9df324c7"
 
-supports-color@^4.0.0:
-  version "4.4.0"
-  resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-4.4.0.tgz#883f7ddabc165142b2a61427f3352ded195d1a3e"
-  dependencies:
-    has-flag "^2.0.0"
-
 sw-precache@^5.1.1, sw-precache@^5.2.0:
   version "5.2.0"
   resolved "https://registry.yarnpkg.com/sw-precache/-/sw-precache-5.2.0.tgz#eb6225ce580ceaae148194578a0ad01ab7ea199c"
@@ -8372,6 +8419,10 @@ yallist@^2.1.2:
   version "2.1.2"
   resolved "https://registry.yarnpkg.com/yallist/-/yallist-2.1.2.tgz#1c11f9218f076089a47dd512f93c6699a6a81d52"
 
+yallist@^3.0.0:
+  version "3.0.2"
+  resolved "https://registry.yarnpkg.com/yallist/-/yallist-3.0.2.tgz#8452b4bb7e83c7c188d8041c1a837c773d6d8bb9"
+
 yargs@~3.10.0:
   version "3.10.0"
   resolved "https://registry.yarnpkg.com/yargs/-/yargs-3.10.0.tgz#f7ee7bd857dd7c1d2d38c0e74efbd681d1431fd1"