Test Case Generation Benefits
By extending JUnit with Jtest, you can automatically generate JUnit-compatible test cases that verify code construction, stability, and—if the class uses Eiffel Software's Design by Contract—functionality. This allows you to generate a foundational test suite you can extend with JUnit test classes.

Jtest's automatic test case generation helps you prevent errors in two main ways:

1. It enables you to quickly produce all the required test cases for thorough construction testing, which is impractical to achieve manually. Jtest tries to create test cases that execute every possible branch of each method it tests. For example, if the method contains a conditional statement (such as an if block), Jtest will generate test cases that test the true and false outcomes of the if statement.
2. It enables you to instantly generate and execute test cases as soon as you are done writing or modifying a class. This prompts you to find and fix problems before you (or a team member) unwittingly introduce additional errors by adding code that builds upon or interacts with the problematic code.

Static Analysis Benefits
Jtest's static analysis feature provides additional error-prevention safeguards. During testing, Jtest will statically analyze each class by parsing its Java source code and checking whether it follows a set of over 300 coding guidelines or "rules" designed to identify error-prone code. You can also design and enforce custom coding guidelines as needed. Each time you find an error, you can determine why the error occurred, develop a custom rule that prohibits the cause of this problem, then automatically enforce this rule to ensure that Jtest immediately identifies any repeat offenses.

If you relied only on JUnit, you might start the testing process by creating a test class like the one shown in Listing 2.

If you compile this test class then execute it using JUnit, all the test cases will pass. You probably would then check the source code into the source code repository and begin working on the next class.

However, if you use both Jtest and JUnit in this scenario, you would perform the following steps:

1. Load Simple.class into the Jtest Class Testing UI.
2. Click the Start tool bar button to start the test (as shown in Figure 1).

Figure 1: Testing Simple.class in Jtest

Jtest examines the class under test, statically analyzes the class's source code, designs test cases that test the class's construction and attempt to cover every branch of every method, and then executes both the automatically generated test cases and the six JUnit test cases represented in the SimpleTest test class. This entire process takes less than 25 seconds. If the class contained Design by Contract comments, Jtest would have also designed test cases that verify the class's functionality.

When the test is completed, Jtest reports the results shown in Figure 2.

Figure 2: The Results of the Simple.class Test

By using Jtest with JUnit, you identified 12 violations of Java coding guidelines and one uncaught runtime exception. In addition, you gained 15 new test cases that you can export as a JUnit test class and/or use for functionality testing.

Figure 3: A Runtime Exception that Jtest Exposed

The violation of the PB.TLS static analysis rule shown in Figure 4 reveals that the developer of this class inadvertently wrote case10 instead of case 10. If the class is not fixed, it will give incorrect results when it is passed the value 10. If this problem is allowed to remain in the code, it will likely cause strange, difficult-to-diagnose errors during application testing or in the field. Once again, by identifying and fixing this problem immediately, you can prevent grief later.

Figure 4: A Coding Standard Violation that Jtest Identified

Create a JUnit-compatible Test Class for Automatically Generated Test Cases
Finally, assume that you want to create a JUnit test class that represents the 15 automatically generated test cases. You choose Jtest's Export to a JUnit Test Class option. Jtest instantly generates a test class that allows you to run these 15 test cases in either Jtest or JUnit. You can add more functional test cases by modifying the test methods in the automatically generated test class, and then you can run the modified test class in either Jtest or JUnit. Adding test cases in this manner enables you to verify whether the class is correct. This strategy significantly reduces the amount of code that you need to write for each test—without sacrificing test quality.

Integrate Unit Testing into Daily Development
These days, almost every Java developer recognizes the value of practices such as unit testing and coding standard enforcement, and intends to perform them as part of his or her regular testing practices. However, these practices can be time-consuming, and most developers rarely have the opportunity to perform them as early, frequently, or thoroughly as they would like. Extending JUnit with Jtest can solve this problem. When you use both Jtest and JUnit, you can realistically integrate unit testing and coding standard enforcement into your daily development practices.