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How to test methods that call System.exit()?

Asked 2008-11-21T16:38:58.930
242

I've got a few methods that should call System.exit() on certain inputs. Unfortunately, testing these cases causes JUnit to terminate! Putting the method calls in a new Thread doesn't seem to help, since System.exit() terminates the JVM, not just the current thread. Are there any common patterns for dealing with this? For example, can I substitute a stub for System.exit()?

The class in question is actually a command-line tool which I'm attempting to test inside JUnit. Maybe JUnit is simply not the right tool for the job? Suggestions for complementary regression testing tools are welcome (preferably something that integrates well with JUnit and EclEmma).

java multithreading unit-testing junit testability
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32

You actually can mock or stub out the System.exit method, in a JUnit test.

For example, using JMockit you could write (there are other ways as well):

@Test
public void mockSystemExit(@Mocked("exit") System mockSystem)
{
    // Called by code under test:
    System.exit(); // will not exit the program
}


EDIT: Alternative test (using latest JMockit API) which does not allow any code to run after a call to System.exit(n):

@Test(expected = EOFException.class)
public void checkingForSystemExitWhileNotAllowingCodeToContinueToRun() {
    new Expectations(System.class) {{ System.exit(anyInt); result = new EOFException(); }};

    // From the code under test:
    System.exit(1);
    System.out.println("This will never run (and not exit either)");
}
answered 2009-07-26T18:27:49.360

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