Test if an exception is caught with Junit

I’ll begin with a code example; I have to test a function, which handles data-packets. In this function, the data-packet is opened and when it doesn’t contain all expected data, an InvalidParameterExeption is thrown which is logged.

public void handleData(dataPacket) {
    try {
        analyseData(dataPacket);
    } catch (InvalidParameterException e) {
        e.printStackTrace()
    }
}

So, if everything goes well, my exception is printed in my terminal. But how can I test this? I can’t use this: (because the exception is caught)

@Test(expected = InvalidParameterExeption.class)
public void testIfFaultyDataPacketIsRecognised {
    handleData(faultyDataPacket);
}

How can I test that the InvalidParameterExeption is thrown?

Answer

You won’t catch exceptions that are not thrown. Just test the ‘throwing exception’ method instead of the ‘exception catching’ one

@Test(expected = InvalidParameterExeption.class)
public void testIfFaultyDataPacketIsRecognised() {
    analyseData(faultyDataPacket);
}