diff -r 000000000000 -r 6474c204b198 browser/devtools/canvasdebugger/test/browser_canvas-frontend-stepping.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/canvasdebugger/test/browser_canvas-frontend-stepping.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,76 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Tests if the stepping buttons in the call list toolbar work as advertised.
+ */
+
+function ifTestingSupported() {
+  let [target, debuggee, panel] = yield initCanavsDebuggerFrontend(SIMPLE_CANVAS_URL);
+  let { window, $, EVENTS, SnapshotsListView, CallsListView } = panel.panelWin;
+
+  yield reload(target);
+
+  let recordingFinished = once(window, EVENTS.SNAPSHOT_RECORDING_FINISHED);
+  let callListPopulated = once(window, EVENTS.CALL_LIST_POPULATED);
+  SnapshotsListView._onRecordButtonClick();
+  yield promise.all([recordingFinished, callListPopulated]);
+
+  checkSteppingButtons(1, 1, 1, 1);
+  is(CallsListView.selectedIndex, -1,
+    "There should be no selected item in the calls list view initially.");
+
+  CallsListView._onResume();
+  checkSteppingButtons(1, 1, 1, 1);
+  is(CallsListView.selectedIndex, 0,
+    "The first draw call should now be selected.");
+
+  CallsListView._onResume();
+  checkSteppingButtons(1, 1, 1, 1);
+  is(CallsListView.selectedIndex, 2,
+    "The second draw call should now be selected.");
+
+  CallsListView._onStepOver();
+  checkSteppingButtons(1, 1, 1, 1);
+  is(CallsListView.selectedIndex, 3,
+    "The next context call should now be selected.");
+
+  CallsListView._onStepOut();
+  checkSteppingButtons(0, 0, 1, 0);
+  is(CallsListView.selectedIndex, 7,
+    "The last context call should now be selected.");
+
+  function checkSteppingButtons(resume, stepOver, stepIn, stepOut) {
+    if (!resume) {
+      is($("#resume").getAttribute("disabled"), "true",
+        "The resume button doesn't have the expected disabled state.");
+    } else {
+      is($("#resume").hasAttribute("disabled"), false,
+        "The resume button doesn't have the expected enabled state.");
+    }
+    if (!stepOver) {
+      is($("#step-over").getAttribute("disabled"), "true",
+        "The stepOver button doesn't have the expected disabled state.");
+    } else {
+      is($("#step-over").hasAttribute("disabled"), false,
+        "The stepOver button doesn't have the expected enabled state.");
+    }
+    if (!stepIn) {
+      is($("#step-in").getAttribute("disabled"), "true",
+        "The stepIn button doesn't have the expected disabled state.");
+    } else {
+      is($("#step-in").hasAttribute("disabled"), false,
+        "The stepIn button doesn't have the expected enabled state.");
+    }
+    if (!stepOut) {
+      is($("#step-out").getAttribute("disabled"), "true",
+        "The stepOut button doesn't have the expected disabled state.");
+    } else {
+      is($("#step-out").hasAttribute("disabled"), false,
+        "The stepOut button doesn't have the expected enabled state.");
+    }
+  }
+
+  yield teardown(panel);
+  finish();
+}