diff --git a/cssom/insertRule-charset-no-index.html b/cssom/insertRule-charset-no-index.html
new file mode 100644
index 00000000000000..b94dc11afae7c4
--- /dev/null
+++ b/cssom/insertRule-charset-no-index.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>CSS Test: CSSOM StyleSheet insertRule with charset and omitted second argument</title>
+    <link rel="author" title="Sendil Kumar N" href="mailto:sendilkumarn.opensource@gmail.com">
+    <link rel="help" href="https://drafts.csswg.org/cssom/">
+    <link rel="help" href="http://www.w3.org/TR/cssom-1/#the-cssrule-interface">
+    <meta name="flags" content="dom">
+    <script src="/resources/testharness.js" type="text/javascript"></script>
+    <script src="/resources/testharnessreport.js" type="text/javascript"></script>
+    <link rel="stylesheet" type="text/css" href="support/import-charset.css" id="linkElement" >
+</head>
+<body>
+<div id="log"></div>
+<script type="text/javascript">
+    var sheet = document.getElementById("linkElement").sheet;
+    test(function() {
+        assert_equals(sheet.cssRules.length, 0);
+        sheet.insertRule("p { color: green; }");
+        assert_equals(sheet.cssRules.length, 1);
+        assert_equals(sheet.cssRules.item(0).cssText, "p { color: green; }");
+    }, "inserRule with charset and omitted index argument");
+
+    test(function() {
+        assert_equals(sheet.cssRules.length, 1);
+        sheet.insertRule("p { color: yellow; }", undefined);
+        assert_equals(sheet.cssRules.length, 2);
+        assert_equals(sheet.cssRules.item(0).cssText, "p { color: yellow; }");
+    }, "insertRule with charset and undefined index argument");
+</script>
+</body>
+</html>
diff --git a/cssom/insertRule-import-no-index.html b/cssom/insertRule-import-no-index.html
new file mode 100644
index 00000000000000..c97d3949487026
--- /dev/null
+++ b/cssom/insertRule-import-no-index.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>CSS Test: CSSOM StyleSheet insertRule with import and omitted second argument</title>
+    <link rel="author" title="Sendil Kumar N" href="mailto:sendilkumarn.opensource@gmail.com">
+    <link rel="help" href="https://drafts.csswg.org/cssom/">
+    <link rel="help" href="http://www.w3.org/TR/cssom-1/#the-cssrule-interface">
+    <meta name="flags" content="dom">
+    <script src="/resources/testharness.js" type="text/javascript"></script>
+    <script src="/resources/testharnessreport.js" type="text/javascript"></script>
+    <style id="styleElement">
+        @import url("support/a-green.css");
+    </style>
+</head>
+<body>
+<div id="log"></div>
+<script type="text/javascript">
+    var sheet = document.getElementById("styleElement").sheet;
+    test(function() {
+        assert_equals(sheet.cssRules.length, 1);
+        assert_throws("HierarchyRequestError", function() { sheet.insertRule("p { color: green; }"); });
+        assert_equals(sheet.cssRules.length, 1);
+    }, "inserRule with import and omitted index argument");
+
+    test(function() {
+        assert_equals(sheet.cssRules.length, 1);
+        assert_throws("HierarchyRequestError", function() { sheet.insertRule("p { color: yellow; }", undefined); });
+        assert_equals(sheet.cssRules.length, 1);
+        assert_equals(sheet.cssRules.item(0).cssText, "@import url(\"support/a-green.css\");");
+    }, "insertRule with import and undefined index argument");
+</script>
+</body>
+</html>
diff --git a/cssom/insertRule-namespace-no-index.html b/cssom/insertRule-namespace-no-index.html
new file mode 100644
index 00000000000000..8a3315d860611d
--- /dev/null
+++ b/cssom/insertRule-namespace-no-index.html
@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>CSS Test: CSSOM StyleSheet insertRule with namespace and omitted second argument</title>
+    <link rel="author" title="Sendil Kumar N" href="mailto:sendilkumarn.opensource@gmail.com">
+    <link rel="help" href="https://drafts.csswg.org/cssom/">
+    <link rel="help" href="http://www.w3.org/TR/cssom-1/#the-cssrule-interface">
+    <meta name="flags" content="dom">
+    <script src="/resources/testharness.js" type="text/javascript"></script>
+    <script src="/resources/testharnessreport.js" type="text/javascript"></script>
+    <style id="styleElement">
+        @namespace svg url(http://servo);
+        @namespace url(http://servo1);
+        @namespace svg url("http://servo2");
+    </style>
+</head>
+<body>
+<div id="log"></div>
+<script type="text/javascript">
+    var sheet = document.getElementById("styleElement").sheet;
+    test(function() {
+        assert_equals(sheet.cssRules.length, 3);
+        assert_throws("HierarchyRequestError", function() { sheet.insertRule("p { color: green; }"); });
+        assert_equals(sheet.cssRules.length, 3);
+    }, "inserRule with namespace and omitted index argument");
+
+    test(function() {
+        assert_equals(sheet.cssRules.length, 3);
+        assert_throws("HierarchyRequestError", function() { sheet.insertRule("p { color: yellow; }", undefined); });
+        assert_equals(sheet.cssRules.length, 3);
+    }, "insertRule with namespace and undefined index argument");
+
+    test(function() {
+        assert_equals(sheet.cssRules.length, 3);
+        sheet.insertRule("@import url(\"support/a-green.css\");");
+        assert_equals(sheet.cssRules.length, 4);
+    }, "inserRule with namespace and omitted index argument should insert import");
+</script>
+</body>
+</html>
diff --git a/cssom/insertRule-no-index.html b/cssom/insertRule-no-index.html
new file mode 100644
index 00000000000000..c9704b7475a5fe
--- /dev/null
+++ b/cssom/insertRule-no-index.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>CSS Test: CSSOM StyleSheet insertRule omitted second argument</title>
+    <link rel="author" title="Sendil Kumar N" href="mailto:sendilkumarn.opensource@gmail.com">
+    <link rel="help" href="https://drafts.csswg.org/cssom/">
+    <link rel="help" href="http://www.w3.org/TR/cssom-1/#the-cssrule-interface">
+    <meta name="flags" content="dom">
+    <script src="/resources/testharness.js" type="text/javascript"></script>
+    <script src="/resources/testharnessreport.js" type="text/javascript"></script>
+    <style id="styleElement">
+        /* An initial style rule to test where the new rule is inserted relative to this one */
+        nosuchelement { color: red; }
+    </style>
+</head>
+<body>
+<div id="log"></div>
+<script type="text/javascript">
+    var sheet = document.getElementById("styleElement").sheet;
+    test(function() {
+        assert_equals(sheet.cssRules.length, 1);
+        sheet.insertRule("p { color: green; }");
+        assert_equals(sheet.cssRules.length, 2);
+        assert_equals(sheet.cssRules.item(0).cssText, "p { color: green; }");
+    }, "inserRule with omitted index argument");
+
+    test(function() {
+        assert_equals(sheet.cssRules.length, 2);
+        sheet.insertRule("p { color: yellow; }", undefined);
+        assert_equals(sheet.cssRules.length, 3);
+        assert_equals(sheet.cssRules.item(0).cssText, "p { color: yellow; }");
+    }, "insertRule with undefined index argument");
+</script>
+</body>
+</html>
diff --git a/cssom/support/import-charset.css b/cssom/support/import-charset.css
new file mode 100644
index 00000000000000..9f44090c94a794
--- /dev/null
+++ b/cssom/support/import-charset.css
@@ -0,0 +1 @@
+@charset "UTF-8";
