JUnit tests run in eclipse return errors even though I have expected annotation

Question

(This is a follow up question to this one.)

I'm having a problem with JUnit4 tests in eclipse. I'm trying to use the @Test(expected=...) annotation to unit test exception throwing. The problem is that when I run the tests, they come back as errors instead of passing, even though I'm expecting the exceptions to be thrown.

I'm using eclipse 3.4.0 and JUnit 4.3.1.

Here's the code:

Class to test:

public class IPAddress
{
    private byte[] octets;

    private IPAddress()
    {
     octets = new byte[4];
    }

    public IPAddress(String addr) throws InvalidIPAddressException
    {
     this();

     if(addr == null || !isValid(addr))
      throw new InvalidIPAddressException(addr);

        String strOctets[] = addr.split("\\.");

        for (int i = 0; i < strOctets.length; i++)
            octets[i] = Byte.parseByte(strOctets[i]);
    }

    public static boolean isValid(String addr)
    {
        String strOctets[] = addr.split("\\.");

        if (strOctets.length != 4)
            return false;

        for (int i = 0; i < strOctets.length; i++)
        {
            try
            {
                int num = Integer.parseInt(strOctets[i]);

                if (num < 0 || num > 255)
                    return false;
            } catch (NumberFormatException e)
            {
                return false;
            }
        }

        return true;
    }

    public byte[] getOctets()
    {
     return octets;
    }
}

Exception:

public class InvalidIPAddressException extends Exception
{
    public InvalidIPAddressException(String addr)
    {
     super("\"" + addr + "\" is not a valid IP address");
    }
}

Test case:

public class IPAddressTest extends TestCase
{
    @Test(expected=InvalidIPAddressException.class)
    public void testNullParameter() throws InvalidIPAddressException
    {
     @SuppressWarnings("unused")
     IPAddress addr = new IPAddress(null);
     fail("InvalidIPAddressException not thrown.");
    }

    @Test(expected=InvalidIPAddressException.class)
    public void testHostnameParameter() throws InvalidIPAddressException
    {
     @SuppressWarnings("unused")
     IPAddress addr = new IPAddress("http://www.google.com");
     fail("InvalidIPAddressException not thrown.");
    }

    @Test
    public void testValidIPAddress() throws InvalidIPAddressException
    {
     IPAddress addr = new IPAddress("127.0.0.1");
     byte[] octets = addr.getOctets();

     assertTrue(octets[0] == 127);
     assertTrue(octets[1] == 0);
     assertTrue(octets[2] == 0);
     assertTrue(octets[3] == 1);
    }

    public static void main(String[] args)
    {
     TestRunner.run(IPAddressTest.class);
    }
}

Answer 1

Likely because when you try to instantiate the InvalidIPAddressException the constructor throw a NullPointerException when it tries to concatenate the string in it.

public InvalidIPAddressException(String addr)
{
    super("\"" + addr + "\" is not a valid IP address"); // NPE while concatenate
}

Answer 2

It looks like you're mixing up JUnit 3 and 4 code. TestRunner is part of JUnit 3, so doesn't look at the annotations at all.

Try removing extends TestCase and changing TestRunner.run(IPAddressTest.class); to JUnitCore.runClasses(IPAddressTest.class); (you'll need to add the imports as required).