diff -r 000000000000 -r 6474c204b198 dom/camera/test/camera_common.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/camera/test/camera_common.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,143 @@
+var CameraTest = (function() {
+  'use strict';
+
+  /**
+   * 'camera.control.test.enabled' is queried in Gecko to enable different
+   * test modes in the camera stack. The only currently-supported setting
+   * is 'hardware', which wraps the Gonk camera abstraction class in a
+   * shim class that supports injecting hardware camera API failures into
+   * the execution path.
+   *
+   * The affected API is specified by the 'camera.control.test.hardware'
+   * pref. Currently supported values should be determined by inspecting
+   * TestGonkCameraHardware.cpp.
+   *
+   * Some API calls are simple: e.g. 'start-recording-failure' will cause
+   * the DOM-facing startRecording() call to fail. More complex tests like
+   * 'take-picture-failure' will cause the takePicture() API to fail, while
+   * 'take-picture-process-failure' will simulate a failure of the
+   * asynchronous picture-taking process, even if the initial API call
+   * path seems to have succeeded.
+   *
+   * If 'camera.control.test.hardware.gonk.parameters' is set, it will cause
+   * the contents of that string to be appended to the string of parameters
+   * pulled from the Gonk camera library. This allows tests to inject fake
+   * settings/capabilities for features not supported by the emulator. These
+   * parameters are one or more semicolon-delimited key=value pairs, e.g. to
+   * pretend the emulator supports zoom:
+   *
+   *   zoom-ratios=100,150,200,300,400;max-zoom=4
+   *
+   * This means (of course) that neither the key not the value tokens can
+   * contain either equals signs or semicolons. The test shim doesn't enforce
+   * this so that we can test getting junk from the camera library as well.
+   */
+  const PREF_TEST_ENABLED = "camera.control.test.enabled";
+  const PREF_TEST_HARDWARE = "camera.control.test.hardware";
+  const PREF_TEST_EXTRA_PARAMETERS = "camera.control.test.hardware.gonk.parameters";
+  var oldTestEnabled;
+  var oldTestHw;
+  var testMode;
+
+  function testHardwareSetFakeParameters(parameters, callback) {
+    SpecialPowers.pushPrefEnv({'set': [[PREF_TEST_EXTRA_PARAMETERS, parameters]]}, function() {
+      var setParams = SpecialPowers.getCharPref(PREF_TEST_EXTRA_PARAMETERS);
+      ise(setParams, parameters, "Extra test parameters '" + setParams + "'");
+      if (callback) {
+        callback(setParams);
+      }
+    });
+  }
+
+  function testHardwareClearFakeParameters(callback) {
+    SpecialPowers.pushPrefEnv({'clear': [[PREF_TEST_EXTRA_PARAMETERS]]}, callback);
+  }
+
+  function testHardwareSet(test, callback) {
+    SpecialPowers.pushPrefEnv({'set': [[PREF_TEST_HARDWARE, test]]}, function() {
+      var setTest = SpecialPowers.getCharPref(PREF_TEST_HARDWARE);
+      ise(setTest, test, "Test subtype set to " + setTest);
+      if (callback) {
+        callback(setTest);
+      }
+    });
+  }
+
+  function testHardwareDone(callback) {
+    testMode = null;
+    if (oldTestHw) {
+      SpecialPowers.pushPrefEnv({'set': [[PREF_TEST_HARDWARE, oldTestHw]]}, callback);
+    } else {
+      SpecialPowers.pushPrefEnv({'clear': [[PREF_TEST_HARDWARE]]}, callback);
+    }
+  }
+
+  function testBegin(mode, callback) {
+    SimpleTest.waitForExplicitFinish();
+    try {
+      oldTestEnabled = SpecialPowers.getCharPref(PREF_TEST_ENABLED);
+    } catch(e) { }
+    SpecialPowers.pushPrefEnv({'set': [[PREF_TEST_ENABLED, mode]]}, function() {
+      var setMode = SpecialPowers.getCharPref(PREF_TEST_ENABLED);
+      ise(setMode, mode, "Test mode set to " + setMode);
+      if (setMode === "hardware") {
+        try {
+          oldTestHw = SpecialPowers.getCharPref(PREF_TEST_HARDWARE);
+        } catch(e) { }
+        testMode = {
+          set: testHardwareSet,
+          setFakeParameters: testHardwareSetFakeParameters,
+          clearFakeParameters: testHardwareClearFakeParameters,
+          done: testHardwareDone
+        };
+        if (callback) {
+          callback(testMode);
+        }
+      }
+    });
+  }
+
+  function testEnd(callback) {
+    // A chain of clean-up functions....
+    function allCleanedUp() {
+      SimpleTest.finish();
+      if (callback) {
+        callback();
+      }
+    }
+    function cleanUpTestEnabled() {
+      var next = allCleanedUp;
+      if (oldTestEnabled) {
+        SpecialPowers.pushPrefEnv({'set': [[PREF_TEST_ENABLED, oldTestEnabled]]}, next);
+      } else {
+        SpecialPowers.pushPrefEnv({'clear': [[PREF_TEST_ENABLED]]}, next);
+      }
+    }
+    function cleanUpTest() {
+      var next = cleanUpTestEnabled;
+      if (testMode) {
+        testMode.done(next);
+        testMode = null;
+      } else {
+        next();
+      }
+    }
+    function cleanUpExtraParameters() {
+      var next = cleanUpTest;
+      if (testMode) {
+        testMode.clearFakeParameters(next);
+      } else {
+        next();
+      }
+    }
+
+    cleanUpExtraParameters();
+  }
+
+  ise(SpecialPowers.sanityCheck(), "foo", "SpecialPowers passed sanity check");
+  return {
+    begin: testBegin,
+    end: testEnd
+  };
+
+})();