Testing a Windows Forms Application
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Welcome to the conclusion of a five-part article series on how to code and test a Windows Forms application. In this part, we finally test our project. This article is excerpted from chapter three of
Murach's Visual Basic 2008, written by Anne Boehm (Murach, 2008; ISBN: 1890774456).
How to test a project
When you test a project, you run it and make sure the application works correctly. As you test your project, you should try every possible combination of input data and user actions to be certain that the project works correctly in every case. In other words, your goal is to make the project fail. Figure 3-17 provides an overview of the testing process for Visual Basic applications.
To start, you should test the user interface. Make sure that each control is sized and positioned properly, that there are no spelling errors in any of the controls or in the form’s title bar, and that the navigation features such as the tab order and access keys work properly.
Next, subject your application to a carefully thought-out sequence of valid test data. Make sure you test every combination of data that the project will handle. If, for example, the project calculates the discount at different values based on the value of the subtotal, use subtotals that fall within each range.
Finally, test the program to make sure that it properly handles invalid data entered by users. For example, type text information into text boxes that expect numeric data. Leave fields blank. Use negative numbers where they shouldn’t be allowed. Remember that the goal of testing is to find all of the problems.
As you test your projects, you’ll encounter runtime errors. These errors, also known as exceptions, occur when Visual Basic encounters a problem that prevents a statement from being executed. If, for example, a user enters “ABC” into the Subtotal text box on the Invoice Total form, a runtime error will occur when the program tries to assign that value to a decimal variable.
When a runtime error occurs, Visual Studio breaks into the debugger and displays an Exception Assistant window like the one in this figure. Then, you can use the debugging tools that you’ll be introduced to in the next figure to debug the error.
Runtime errors, though, should only occur when you’re testing a program. Before an application is put into production, it should be coded and tested so all runtime errors are caught by the application and appropriate messages are displayed to the user. You’ll learn how to do that in chapter 7 of this book.
The Exception Assistant that’s displayed when a runtime error occurs
How to test a project
Test the user interface. Visually check all the controls to make sure they are displayed properly with the correct text. Use the Tab key to make sure the tab order is set correctly, verify that the access keys work right, and make sure that the Enter and Esc keys work properly.
Test valid input data. For example, enter data that you would expect a user to enter.
Test invalid data or unexpected user actions. For example, leave required fields blank, enter text data into numeric input fields, and use negative numbers where they are not appropriate. Try everything you can think of to make the application fail.
Description
To test a project, you run the project to make sure it works properly no matter what combinations of valid or invalid data you enter or what sequence of controls you use.
If a statement in your application can’t be executed, a runtime error, or exception, occurs. Then, if the exception isn’t handled by your application, the statement that caused the exception is highlighted and an Exception Assistant window like the one above is displayed. At that point, you need to debug the application.
Figure 3-17. How to test a project
Next: How to debug runtime errors >>
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 This article is excerpted from chapter three of Murach's Visual Basic 2008, written by Anne Boehm (Murach, 2008; ISBN: 1890774456). Check it out today at your favorite bookstore. Buy this book now.
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