How to Test Methods that Trigger `System.exit()` Calls in JUnit?

How to Tackle Methods that Trigger System.exit() Calls in JUnit Tests

Testing methods that utilize System.exit() poses challenges in JUnit environments due to the termination of the JVM. To overcome this obstacle, various solutions have been proposed:

Substitute Exceptions for System.exit()

Derkeiler.com suggests abandoning System.exit() and instead throwing unchecked exceptions. While JUnit catches these exceptions, highlighting test failures, it allows for continued execution of subsequent tests.

Modify JUnit to Prevent System.exit()

By implementing a custom TestCase class, NoExitTestCase, a security manager can be employed to block System.exit() calls. Upon triggering an exit attempt, a SecurityException is thrown, enabling the test case to handle and verify the expected exit status.

Leverage System Rules

System Rules introduced in JUnit 4.9 provide a mechanism for testing code that interacts with java.lang.System. The ExpectedSystemExit rule specifically enables verification of System.exit() calls, allowing examination of exit status codes.

Additional Considerations

When testing methods that invoke System.exit() with Java 21 or later, the system property -Djava.security.manager=allow must be set to enable the use of security managers.

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