Testing Methods That Call System.exit() With JUnit

Testing Methods That Call System.exit() with JUnit

When developing applications, a common way to terminate the application is to use the System.exit() method. This method halts the current Java Virtual Machine (JVM) immediately, regardless of any remaining code that needs to be executed. Using this method in the wrong circumstances can lead to hard to track down errors and instability to your program. Therefore it is important to test when and how this method is used in your code.

The JUnit framework is one of the most popular testing frameworks available for Java developers. It is typically used to test individual units of code, but it can also be used to test methods that call system exit. To do this, there are a couple of approaches you can take.

Testing System.exit() with an Assertion

The simplest way to test a method that calls system exit is to use an assertion. An assertion is just a statement which tests if something is true or not. In this case, you would use an assertion to test if the method is calling system exit or not. For example, the following assertion will tell you if the method is calling system exit:

assertEquals(true, myMethod.isExiting());

Using assertions to test for system exit is the most basic approach you can use, but it does have some limitations. It only tells you if the method is calling system exit, it doesn’t tell you why. Additionally, depending on how the method is written, it may not accurately reflect the real-world behaviour of the application.

Testing System.exit() with a Mock

One way to get around the limitations of using assertions to test system exit is to create a mock version of the method which calls system exit. A mock is a simulated version of the method, which allows you to control the behaviour and results of the method in a test environment. To create a mock version of a method, you can use a mocking framework like Mockito.

 Mockito.when(myMethod.isExiting()).thenReturn(true);

Using mocks is a good way to make sure that your tests are accurately reflecting the real-world behaviour of your application. Additionally, it allows you to control the behaviour of the system exit method more precisely in order to test different scenarios.

Conclusion

Testing methods that call system exit is an important part of ensuring the stability and reliability of your application. The JUnit framework can be used to test such methods, either by using assertions or by creating mocks. Whichever approach you decide to take, it is important to make sure that your tests are as comprehensive as possible in order to ensure that your application works as expected.