Modern ASP.NET web applications take full advantage of client-side
JavaScript to provide better interactivity and responsiveness. If you are building an ASP.NET application in the right way, you quickly end up with lots and lots of
JavaScript code. When writing
server code, you should be writing unit tests. One big advantage of unit tests is that they provide you with a safety net that enable you to safely modify your existing code – for example, fix bugs, add new features, and make performance enhancements -- without breaking your existing code. Every time you modify your code, you can execute your unit tests to verify that you have not broken anything. For the same reason that you should write unit tests for your
server code, you should write unit tests for your client code.
JavaScript is just as susceptible to bugs as C#. There is no shortage of unit testing frameworks for
JavaScript. Each of the major
JavaScript libraries has its own unit testing framework. For example, jQuery has QUnit, Prototype has UnitTestJS, YUI has YUI Test, and Dojo has Dojo Objective Harness (DOH). The challenge is integrating a
JavaScript unit testing framework with Visual Studio. Visual Studio and Visual Studio ALM provide fantastic support for server-side unit tests. You can easily view the results of running your unit tests in the Visual Studio Test Results window. You can set up a check-in policy which requires that all unit tests pass before your source code can be committed to the source code repository. In addition, you can set up Team Build to execute your unit tests automatically. Unfortunately, Visual Studio does not provide “out-of-the-box” support for
JavaScript unit tests. MS Test, the unit testing framework included in Visual Studio, does not support
JavaScript unit tests. As soon as you leave the
server world, you are left on your own. The goal of this blog entry is to describe one approach to integrating
JavaScript unit tests with MS Test so that you can execute your
JavaScript unit tests side-by-side with your C# unit tests. The goal is to enable you to execute
JavaScript unit tests in exactly the same way as server-side unit tests. You can download the source code described by this project by scrolling to the end of this blog entry. Rejected Approach: Browser Launchers One popular approach to executing
JavaScript unit tests is to use a browser as a test-driver. When you use a browser as a test-driver, you open up a browser window to execute and view the results of executing your
JavaScript unit tests. For example, QUnit – the unit testing framework for jQuery – takes this approach. The following HTML page illustrates how you can use QUnit to create a unit test for a function named addNumbers(). <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Using QUnit</title>
<link rel="stylesheet" href="http://github.com/jquery/qunit/raw/master/qunit/qunit.css" type="text/css" />
</head>
<body>
<h1 id="qunit-header">QUnit example</h1>
<h2 id="qunit-banner"></h2>
<div id="qunit-testrunner-toolbar"></div>
<h2 id="qunit-userAgent"></h2>
<ol id="qunit-tests"></ol>
<div id="qunit-fixture">test markup, will be hidden</div>
<script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script>
<script type="text/javascript" src="http://github.com/jquery/qunit/raw/master/qunit/qunit.js"></script>
<script type="text/javascript">
// The function to test
function addNumbers(a, b) {
return a+b;
}
// The unit test
test("Test of addNumbers", function () {
equals(4, addNumbers(1,3), "1+3 should be 4");
});
</script>
</body>
</html>
This test verifies that calling addNumbers(1,3) returns the expected value 4. When you open this page in a browser, you can see that this test does, in fact, pass.
The idea is that you can quickly refresh this QUnit HTML
JavaScript test driver page in your browser whenever you modify your
JavaScript code. In other words, you can keep a browser window open and keep refreshing it over and over while you are developing your application. That way, you can know very quickly whenever you have broken your
JavaScript code.
While easy to setup, there are several big disadvantages to this approach to executing
JavaScript unit tests:
You must view your
JavaScript unit test results in a different location than your
server unit test results. The
JavaScript unit test results appear in the browser and the
server unit test results appear in the Visual Studio Test Results window. Because all of your unit test results don’t appear in a single location, you are more likely to introduce bugs into your code without noticing it.
Because your unit tests are not integrated with Visual Studio – in particular, MS Test -- you cannot easily include your
JavaScript unit tests when setting up check-in policies or when performing automated builds with Team Build.
A more sophisticated approach to using a browser as a test-driver is to automate the web browser. Instead of launching the browser and loading the test code yourself, you use a framework to automate this process. There are several different testing frameworks that support this approach:
· Selenium – Selenium is a very powerful framework for automating browser tests. You can create your tests by recording a Firefox session or by writing the test driver code in
server code such as C#. You can learn more about Selenium at http://seleniumhq.org/.
LTAF – The ASP.NET team uses the Lightweight Test Automation Framework to test
JavaScript code in the ASP.NET framework. You can learn more about LTAF by visiting the project home at CodePlex: http://aspnet.codeplex.com/releases/view/35501
jsTestDriver – This framework uses Java to automate the browser. jsTestDriver creates a
server which can be used to automate multiple browsers simultaneously. This project is located at http://code.google.com/p/js-test-driver/
TestSwam – This framework, created by John Resig, uses PHP to automate the browser. Like jsTestDriver, the framework creates a test
server. You can open multiple browsers that are automated by the test
server. Learn more about TestSwarm by visiting the following address: https://github.com/jeresig/testswarm/wiki
Yeti – This is the framework introduced by Yahoo for automating browser tests. Yeti uses server-side
JavaScript and depends on Node.js. Learn more about Yeti at http://www.yuiblog.com/blog/2010/08/25/introducing-yeti-the-yui-easy-testing-interface/
All of these frameworks are great for integration tests – however, they are not the best frameworks to use for unit tests. In one way or another, all of these frameworks depend on executing tests within the context of a “living and breathing” browser.
If you create an ASP.NET Unit Test then Visual Studio will launch a web
server before executing the unit test. Why is launching a web
server so bad? It is not the worst thing in the world. However, it does introduce dependencies that prevent your code from being tested in isolation. One of the defining features of a unit test -- versus an integration test – is that a unit test tests code in isolation.
Another problem with launching a web
server when performing unit tests is that launching a web
server can be slow. If you cannot execute your unit tests quickly, you are less likely to execute your unit tests each and every time you make a code change. You are much more likely to fall into the pit of failure.
Launching a browser when performing a
JavaScript unit test has all of the same disadvantages as launching a web
server when performing an ASP.NET unit test. Instead of testing a unit of
JavaScript code in isolation, you are testing
JavaScript code within the context of a particular browser.
Using the frameworks listed above for integration tests makes perfect sense. However, I want to consider a different approach for creating unit tests for
JavaScript code.
Using Server-Side
JavaScript for
JavaScript Unit Tests
A completely different approach to executing
JavaScript unit tests is to perform the tests outside of any browser. If you really want to test
JavaScript then you should test
JavaScript and leave the browser out of the testing process.
There are several ways that you can execute
JavaScript on the
server outside the context of any browser:
Rhino – Rhino is an implementation of
JavaScript written in Java. The Rhino project is maintained by the Mozilla project. Learn more about Rhino at http://www.mozilla.org/rhino/
V8 – V8 is the open-source Google
JavaScript engine written in C++. This is the
JavaScript engine used by the Chrome web browser. You can download V8 and embed it in your project by visiting http://code.google.com/p/v8/
JScript – JScript is the
JavaScript Script Engine used by Internet Explorer (up to but not including Internet Explorer 9), Windows Script Host, and Active
Server Pages.
Internet Explorer is still the most popular web browser. Therefore, I decided to focus on using the JScript Script Engine to execute
JavaScript unit tests.
Using the Microsoft Script Control
There are two basic ways that you can pass
JavaScript to the JScript Script Engine and execute the code: use the Microsoft Windows Script Interfaces or use the Microsoft Script Control.
The difficult and proper way to execute
JavaScript using the JScript Script Engine is to use the Microsoft Windows Script Interfaces. You can learn more about the Script Interfaces by visiting http://msdn.microsoft.com/en-us/library/t9d4xf28(VS.85).aspx
The main disadvantage of using the Script Interfaces is that they are difficult to use from .NET. There is a great series of articles on using the Script Interfaces from C# located at http://www.drdobbs.com/184406028.
I picked the easier alternative and used the Microsoft Script Control. The Microsoft Script Control is an ActiveX control that provides a higher level abstraction over the Window Script Interfaces.
You can download the Microsoft Script Control from here:
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=d7e31492-2595-49e6-8c02-1426fec693ac
After you download the Microsoft Script Control, you need to add a reference to it to your project. Select the Visual Studio menu option Project, Add Reference to open the Add Reference dialog. Select the COM tab and add the Microsoft Script Control 1.0.
Using the Script Control is easy. You call the Script Control AddCode() method to add
JavaScript code to the Script Engine. Next, you call the Script Control Run() method to run a particular
JavaScript function.
The reference documentation for the Microsoft Script Control is located at the MSDN website:
http://msdn.microsoft.com/en-us/library/aa227633%28v=vs.60%29.aspx
Creating the
JavaScript Code to Test
To keep things simple, let’s imagine that you want to test the following
JavaScript function named addNumbers() which simply adds two numbers together:
MvcApplication1\Scripts\Math.js
function addNumbers(a, b) {
return 5;
}
Notice that the addNumbers() method always returns the value 5. Right-now, it will not pass a good unit test.
Create this file and save it in your project with the name Math.js in your MVC project’s Scripts folder (Save the file in your actual MVC application and not your MVC test application).
Creating the
JavaScript Test Helper Class
To make it easier to use the Microsoft Script Control in unit tests, we can create a helper class. This class contains two methods:
LoadFile() – Loads a
JavaScript file. Use this method to load the
JavaScript file being tested or the
JavaScript file containing the unit tests.
ExecuteTest() – Executes the
JavaScript code. Use this method to execute a
JavaScript unit test.
Here’s the code for the JavaScriptTestHelper class:
JavaScriptTestHelper.cs
using System;
using System.IO;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using MSScriptControl;
namespace MvcApplication1.Tests {
public class JavaScriptTestHelper : IDisposable {
private ScriptControl _sc;
private TestContext _context;
/// <summary>
/// You need to use this helper with Unit Tests and not
/// Basic Unit Tests because you need a Test Context
/// </summary>
/// <param name="testContext">Unit Test Test Context</param>
public JavaScriptTestHelper(TestContext testContext) {
if (testContext == null) {
throw new ArgumentNullException("TestContext");
}
_context = testContext;
_sc = new ScriptControl();
_sc.Language = "JScript";
_sc.AllowUI = false;
}
/// <summary>
/// Load the contents of a
JavaScript file into the
/// Script Engine.
/// </summary>
/// <param name="path">Path to
JavaScript file</param>
public void LoadFile(string path) {
var fileContents = File.ReadAllText(path);
_sc.AddCode(fileContents);
}
/// <summary>
/// Pass the path of the test that you want to execute.
/// </summary>
/// <param name="testMethodName">JavaScript function name</param>
public void ExecuteTest(string testMethodName) {
dynamic result = null;
try {
result = _sc.Run(testMethodName, new object[] { });
} catch {
var error = ((IScriptControl)_sc).Error;
if (error != null) {
var description = error.Description;
var line = error.Line;
var column = error.Column;
var text = error.Text;
var source = error.Source;
if (_context != null) {
var details = String.Format("{0} \r\nLine: {1} Column: {2}", source, line, column);
_context.WriteLine(details);
}
}
throw new AssertFailedException(error.Description);
}
}
public void Dispose() {
_sc = null;
}
}
}
Notice that the JavaScriptTestHelper class requires a Test Context to be instantiated. For this reason, you can use the JavaScriptTestHelper only with a Visual Studio Unit Test and not a Basic Unit Test (These are two different types of Visual Studio project items).
Add the JavaScriptTestHelper file to your MVC test application (for example, MvcApplication1.Tests).
Creating the
JavaScript Unit Test
Next, we need to create the
JavaScript unit test function that we will use to test the addNumbers() function. Create a folder in your MVC test project named JavaScriptTests and add the following
JavaScript file to this folder:
MvcApplication1.Tests\JavaScriptTests\MathTest.js
/// <reference path="JavaScriptUnitTestFramework.js"/>
function testAddNumbers() {
// Act
var result = addNumbers(1, 3);
// Assert
assert.areEqual(4, result, "addNumbers did not return right value!");
}
The testAddNumbers() function takes advantage of another
JavaScript library named JavaScriptUnitTestFramework.js. This library contains all of the code necessary to make assertions. Add the following JavaScriptnitTestFramework.js to the same folder as the MathTest.js file:
MvcApplication1.Tests\JavaScriptTests\JavaScriptUnitTestFramework.js
var assert = {
areEqual: function (expected, actual, message) {
if (expected !== actual) {
throw new Error("Expected value " + expected
+ " is not equal to " + actual + ". " + message);
}
}
};
There is only one type of assertion supported by this file: the areEqual() assertion. Most likely, you would want to add additional types of assertions to this file to make it easier to write your
JavaScript unit tests.
Deploying the
JavaScript Test Files
This step is non-intuitive. When you use Visual Studio to run unit tests, Visual Studio creates a new folder and executes a copy of the files in your project. After you run your unit tests, your Visual Studio Solution will contain a new folder named TestResults that includes a subfolder for each test run.
You need to configure Visual Studio to deploy your
JavaScript files to the test run folder or Visual Studio won’t be able to find your
JavaScript files when you execute your unit tests. You will get an error that looks something like this when you attempt to execute your unit tests:
You can configure Visual Studio to deploy your
JavaScript files by adding a Test Settings file to your Visual Studio Solution. It is important to understand that you need to add this file to your Visual Studio Solution and not a particular Visual Studio project. Right-click your Solution in the Solution Explorer window and select the menu option Add, New Item. Select the Test Settings item and click the Add button.
After you create a Test Settings file for your solution, you can indicate that you want a particular folder to be deployed whenever you perform a test run. Select the menu option Test, Edit Test Settings to edit your test configuration file. Select the Deployment tab and select your MVC test project’s JavaScriptTest folder to deploy.
Click the Apply button and the Close button to save the changes and close the dialog.
Creating the Visual Studio Unit Test
The very last step is to create the Visual Studio unit test (the MS Test unit test). Add a new unit test to your MVC test project by selecting the menu option Add New Item and selecting the Unit Test project item (Do not select the Basic Unit Test project item):
The difference between a Basic Unit Test and a Unit Test is that a Unit Test includes a Test Context. We need this Test Context to use the JavaScriptTestHelper class that we created earlier.
Enter the following test method for the new unit test:
[TestMethod]
public void TestAddNumbers() {
var jsHelper = new JavaScriptTestHelper(this.TestContext);
// Load
JavaScript files
jsHelper.LoadFile("JavaScriptUnitTestFramework.js");
jsHelper.LoadFile(@"..\..\..\MvcApplication1\Scripts\Math.js");
jsHelper.LoadFile("MathTest.js");
// Execute
JavaScript Test
jsHelper.ExecuteTest("testAddNumbers");
}
This code uses the JavaScriptTestHelper to load three files:
JavaScripUnitTestFramework.js – Contains the assert functions.
Math.js – Contains the addNumbers() function from your MVC application which is being tested.
MathTest.js – Contains the
JavaScript unit test function.
Next, the test method calls the JavaScriptTestHelper ExecuteTest() method to execute the testAddNumbers()
JavaScript function.
Running the Visual Studio
JavaScript Unit Test
After you complete all of the steps described above, you can execute the
JavaScript unit test just like any other unit test. You can use the keyboard combination CTRL-R, CTRL-A to run all of the tests in the current Visual Studio Solution. Alternatively, you can use the buttons in the Visual Studio toolbar to run the tests:
(Unfortunately, the Run All Impacted Tests button won’t work correctly because Visual Studio won’t detect that your
JavaScript code has changed. Therefore, you should use either the Run Tests in Current Context or Run All Tests in Solution options instead.)
The results of running the
JavaScript tests appear side-by-side with the results of running the
server tests in the Test Results window. For example, if you Run All Tests in Solution then you will get the following results:
Notice that the TestAddNumbers()
JavaScript test has failed. That is good because our addNumbers() function is hard-coded to always return the value 5.
If you double-click the failing
JavaScript test, you can view additional details such as the
JavaScript error message and the line number of the
JavaScript code that failed:
Summary
The goal of this blog entry was to explain an approach to creating
JavaScript unit tests that can be easily integrated with Visual Studio and Visual Studio ALM. I described how you can use the Microsoft Script Control to execute
JavaScript on the
server. By taking advantage of the Microsoft Script Control, we were able to execute our
JavaScript unit tests side-by-side with all of our other unit tests and view the results in the standard Visual Studio Test Results window.
You can download the code discussed in this blog entry from here:
http://StephenWalther.com/downloads/Blog/JavaScriptUnitTesting/JavaScriptUnitTests.zip
Before running this code, you need to first install the Microsoft Script Control which you can download from here:
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=d7e31492-2595-49e6-8c02-1426fec693ac
