In: Root » Computers and technology » AJAX » Testing the Client Side Logic
Problem You want to effectively test your application’s client-side logic. Theory Testing GUI code tends not to be a productive task because of the complications that arise. The main complication is how to test the correctness of a user interface. Imagine a situation where clicking a button causes a table to be filled with data. Now imagine that when a check box is checked and the button is clicked again, a different table is filled with content. The fact that clicking the same button results in two different generated outputs is frustrating and complicates GUI testing. One of the main reasons why testing a GUI is complicated is because the GUI is a black box, and the user cannot access the individual GUI elements. RealPlayer is used to play some media file. Imagine running a media-file generation service. Testing the format of the media is not a problem and is akin to testing the contract. You also need to test if a client such as RealPlayer can consume, process, and display the media. Figuring this out requires taking a snapshot and then checking if the bits and bytes are displayed properly. Thus, you’re left wondering how to test the functionality of your data stream when played in RealPlayer. The simplest but probably most expensive and error-prone solution is to have a human look at RealPlayer and say, “Yes, the content is being played,” or “No, the content has problems.” A human could carry out the same tests repeatedly and then verify whether the tests worked. The problem with getting a human to do this is that humans make errors when doing the same thing over and over again. Humans are not incapable of doing the same thing over and over again, but they get bored and the mind wanders. Humans are much better at spotting problems if the menial work is replaced with automation. Automating the testing of RealPlayer is difficult, because RealPlayer is not under your control. It is programmed using a traditional programming language. Traditional programming languages create black boxes that a user cannot get around. In the old days of Windows 3.1, an application could access another application’s window handles. That ability made it possible to do interesting things, but the cost was that hackers could wreak havoc on an application. Today, applications are not allowed to access another application’s GUI elements willy-nilly. Solution The only effective way to test a GUI is to have access to the source code and test the layer that the GUI calls. The idea is not to test the GUI, but rather to test the logic that the GUI calls. Of course, this only works if the GUI layer contains absolutely no logic and no state. This is more complicated because it means that the GUI is a copy of the state held in memory. Many developers consider this a good thing, and I’m not about to debate the merits or problems of this strategy. Instead, I want to highlight that Ajax and DHTML applications are unique in that they allow you to have your cake and eat it too. With DHTML, two completely unrelated HTML pages can communicate with each other and slice and dice each other’s data. In a traditional programming approach, you wouldn’t like to have other applications changing your look and feel to suit their needs. Yet this is an inherent behavior of DHTML. This feature can be put to good use when creating tests. The browser window in the upper left-hand corner is the test controller, which contains a number of buttons used to test individual features. The test controller button Test Get Document is used open a new instance of the HTML window to be tested. It assigns the instance to the script variable testWindow. When clicked, the button Test Add executes the method TestAdd, which then calls a method DoAdd defined in the new instance of the HTML window. This is a unique feature of DHTML, in that one HTML window can reference elements in another HTML window even though both windows are unrelated. The test controller uses the identical testing routines as outlined in the “Coding the Contract Using Test-Driven Development Techniques” section. The test controller example uses the calculator example. To be able to test the calculator application, copy and modify the empty template file that represents a test. Add the three tests used to verify the correctness of the calculator. There were two unique contracts in the contract recipe. The additional test is the test to open a new window that will load the initial HTML page used to add two numbers. The modification of the template test page involves adding some tests, as well as some user interface elements used to instantiate the tests. I won’t focus on the user interface elements, as the details have already been explained in the “Coding the Contract Using Test-Driven Development Techniques” section. Instead, I’ll focus on the tests that are executed, as they are unique in that they don’t use the XMLHttpRequest object directly. The tests execute functionality in the other HTML page. In the following implementation of the testsToRun variable, note that the declaration has been abbreviated for clarity purposes. |
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