introduce new assertInstanceOf() method

@@ -445,6 +445,22 @@ Asserts that the provided input is of the given type::
 
 .. note:: Type names are always expressed in lower case.
 
+.. index:: InstanceOf
+
+``assertInstanceOf()``
+-------------------------------------------------------------------------------
+
+**Signature:** ``assertInstanceOf(mixed input, String className[, String message])``
+
+Asserts that the provided input is of the given className::
+
+    casper.test.begin('assertInstanceOf() tests', 1, function suite(test) {
+        var daisy = new Cow(){};
+        test.assertInstanceOf(daisy, "Cow", "Okay, daisy is a cow.");
+        test.assertInstanceOf(daisy, "Casper", "Moo is not Boo");
+        test.done();
+    });
+
 .. index:: URL
 
 ``assertUrlMatch()``

@@ -840,6 +840,28 @@ Tester.prototype.assertType = function assertType(subject, type, message) {
 };
 
 /**
+ * Asserts that the provided subject is of the given class name.
+ *
+ * @param  mixed   subject    The value to test
+ * @param  String  className  The javascript class name
+ * @param  String  message    Test description
+ * @return Object             An assertion result object
+ */
+Tester.prototype.assertInstanceOf = function assertInstanceOf(subject, className, message) {
+    "use strict";
+    var actual = subject instanceof className;
+    return this.assert(utils.equals(actual, true), message, {
+        type: "assertType",
+        standard: f('Subject is an instance of: "%s"', className),
+        values: {
+            subject: subject,
+            className: className,
+            actual: actual
+        }
+    });
+};
+
+/**
  * Asserts that a the current page url matches a given pattern. A pattern may be
  * either a RegExp object or a String. The method will test if the URL matches
  * the pattern or contains the String.

@@ -60,6 +60,7 @@ casper.test.begin('Common assertions tests', 45, function(test) {
         test.assertTitleMatch(/test index/, 'Tester.assertTitleMatch() works as expected');
         test.assertTitleMatches(/test index/, 'Tester.assertTitleMatches() works as expected [alias]');
         test.assertType("plop", "string", "Tester.assertType() works as expected");
+        test.assertInstanceOf(casper, "Casper", "Tester.assertInstanceOf() works as expected");
         test.assertUrlMatch(/index\.html$/, "Tester.assertUrlMatch() works as expected");
         test.assertUrlMatches(/index\.html$/, "Tester.assertUrlMatches() works as expected [alias]");
         test.assertVisible('img', 'Tester.assertVisible() works as expected');