All tests are being excluded when using groups in Testng XML suite
===

When I attempt to group my tests in the Testng XML suite, all of the test methods are excluded in the test run. 

I have written my tests in a way that I want all of the test methods in my class to be run, but only certain classes in the suite to be executed, so I have used class level annotations:

    @Test (groups={ TestConstrants.Group1})
    public class ABCTests extends AbstractIntegrationTest
    {
	
        @Test
	public void Test1() throws Exception

        @Test
        public void Test2() throws Exception
    }

    @Test (groups={ TestConstrants.Group2})
    public class DEFTests extends AbstractIntegrationTest
    {
	
        @Test
	public void Test3() throws Exception

        @Test
        public void Test4() throws Exception
    }

My Testng XML is configured for the following:

    <?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd">
    <suite name="SuiteGroup">
      <test name="TestGroups" preserve-order="true">
        <groups>
  		<run>
  			<include name="TestConstants.Group1"/>
  			<exclude name="TestConstants.Group2"/>
  		</run>	
  	</groups>
        <classes>
          <class name="ABCTests"/>
          <class name="DEFTests"/>
        </classes>
      </test> <!-- TestGroups -->
    </suite> <!-- SuiteGroup -->

In this example, I would expect only the tests in class ABCTests to be ran, however, it appears all of the tests are being excluded for some reason. I have verified that the methods in the class I am extending (AbstractIntegrationTest) are set to 'alwaysRun = true'.

I know that I could simply not include the classes that I do not want to run, but I will potentially have hundreds of tests and it is much easier to maintain the test suite by group than class. Any help is greatly appreciated.