diff -r 000000000000 -r 6474c204b198 browser/devtools/markupview/test/browser_markupview_pagesize_01.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/markupview/test/browser_markupview_pagesize_01.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,86 @@
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the markup view loads only as many nodes as specified by the
+// devtools.markup.pagesize preference.
+
+Services.prefs.setIntPref("devtools.markup.pagesize", 5);
+
+const TEST_URL = TEST_URL_ROOT + "doc_markup_pagesize_01.html";
+const TEST_DATA = [{
+  desc: "Select the last item",
+  selector: "#z",
+  expected: "*more*vwxyz"
+}, {
+  desc: "Select the first item",
+  selector: "#a",
+  expected: "abcde*more*"
+}, {
+  desc: "Select the last item",
+  selector: "#z",
+  expected: "*more*vwxyz"
+}, {
+  desc: "Select an already-visible item",
+  selector: "#v",
+  // Because "v" was already visible, we shouldn't have loaded
+  // a different page.
+  expected: "*more*vwxyz"
+}, {
+  desc: "Verify childrenDirty reloads the page",
+  selector: "#w",
+  forceReload: true,
+  // But now that we don't already have a loaded page, selecting
+  // w should center around w.
+  expected: "*more*uvwxy*more*"
+}];
+
+let test = asyncTest(function*() {
+  let {inspector} = yield addTab(TEST_URL).then(openInspector);
+
+  info("Start iterating through the test data");
+  for (let step of TEST_DATA) {
+    info("Start test: " + step.desc);
+
+    if (step.forceReload) {
+      forceReload(inspector);
+    }
+    info("Selecting the node that corresponds to " + step.selector);
+    yield selectNode(step.selector, inspector);
+
+    info("Checking that the right nodes are shwon");
+    assertChildren(step.expected, inspector);
+  }
+
+  info("Checking that clicking the more button loads everything");
+  clickShowMoreNodes(inspector);
+  yield inspector.markup._waitForChildren();
+  assertChildren("abcdefghijklmnopqrstuvwxyz", inspector);
+});
+
+function assertChildren(expected, inspector) {
+  let container = getContainerForRawNode("body", inspector);
+  let found = "";
+  for (let child of container.children.children) {
+    if (child.classList.contains("more-nodes")) {
+      found += "*more*";
+    } else {
+      found += child.container.node.getAttribute("id");
+    }
+  }
+  is(found, expected, "Got the expected children.");
+}
+
+function forceReload(inspector) {
+  let container = getContainerForRawNode("body", inspector);
+  container.childrenDirty = true;
+}
+
+function clickShowMoreNodes(inspector) {
+  let container = getContainerForRawNode("body", inspector);
+  let button = container.elt.querySelector("button");
+  let win = button.ownerDocument.defaultView;
+  EventUtils.sendMouseEvent({type: "click"}, button, win);
+}