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Editorial Team
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Asked: 2026-06-18T15:23:09+00:00

I have a unit test that creates an error condition. Normally, the class under

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I have a unit test that creates an error condition. Normally, the class under test writes this error to the logs (using log4j in this case, but I don’t think that matters). I can change the log level temporarily, using

Logger targetLogger = Logger.getLogger(ClassUnderTest.class);
Level oldLvl = targetLogger.getLevel();
targetLogger.setLevel(Level.FATAL);

theTestObject.doABadThing();

assertTrue(theTestObject.hadAnError());

targetLogger.setLevel(oldLvl);

but that also means that if an unrelated / unintended error occurs during testing, I won’t see that information in the logs either.

Is there a best practice or common pattern I’m supposed to use here? I don’t like prodding the log levels if I can help it, but I also don’t like having a bunch of ERROR noise in the test output, which could scare future developers.

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1 Answer

  1. Editorial Team

    If your logging layer permits, it is a good practice to make an assertion on the error message. You can do it by implementing your own logger that just asserts on the message (without output), or by using a memory-buffer logger and then check on the contents of the log buffer.

    Under no circumstances should the error message end up in the unit-test execution log. This will cause people to get used to errors in the log and mask other errors. In short, your options are:

    1. Most preferred: Catch the message in the harness and assert on it.
    2. Somewhat OK: Raise the level and ignore the message.
    3. Not OK: Don’t do anything and let the log message reach stderr/syslog.
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