diff -r 000000000000 -r 6474c204b198 dom/battery/test/marionette/test_battery_level.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/battery/test/marionette/test_battery_level.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,68 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+MARIONETTE_TIMEOUT = 10000;
+
+let battery = window.navigator.battery;
+
+function verifyInitialState() {
+  ok(battery, "battery");
+  is(battery.level, 0.5, "battery.level");
+  runEmulatorCmd("power display", function (result) {
+    is(result.pop(), "OK", "power display successful");
+    ok(result.indexOf("capacity: 50") !== -1, "power capacity");
+    setUp();
+  });
+}
+
+function unexpectedEvent(event) {
+  ok(false, "Unexpected " + event.type + " event");
+}
+
+function setUp() {
+  battery.onchargingchange = unexpectedEvent;
+  battery.onlevelchange = unexpectedEvent;
+  levelUp();
+}
+
+function changeCapacity(capacity, changeExpected, nextFunction) {
+  log("Changing power capacity to " + capacity);
+  if (changeExpected) {
+    battery.onlevelchange = function (event) {
+     battery.onlevelchange = unexpectedEvent;
+     is(event.type, "levelchange", "event.type");
+     is(battery.level, capacity / 100, "battery.level");
+     nextFunction();
+    };
+    runEmulatorCmd("power capacity " + capacity);
+  }
+  else {
+    runEmulatorCmd("power capacity " + capacity, function () {
+      is(battery.level, capacity / 100, "battery.level");
+      nextFunction();
+    });
+  }
+}
+
+function levelUp() {
+  changeCapacity("90", true, levelDown);
+}
+
+function levelDown() {
+  changeCapacity("10", true, levelSame);
+}
+
+function levelSame() {
+  changeCapacity("10", false, cleanUp);
+}
+
+function cleanUp() {
+  battery.onchargingchange = null;
+  battery.onlevelchange = function () {
+    battery.onlevelchange = null;
+    finish();
+  };
+  runEmulatorCmd("power capacity 50");
+}
+
+verifyInitialState();