Error when function defined as property of TestCase

I'm finding that defining a test case property as a function data type causes some problems.

Here the test case.

package tests
{
    import flexunit.framework.Assert;
   
    public class TestExample
    {       
        public var exampleFn:Function;
       
        [Test]
        public function testExample():void
        {
            Assert.fail("Test method Not yet implemented");
        }
    }
}

Here's the eclipse error.

This seems to stop FlexUnit from working. Can no longer added any other test cases.

I'm running FB4 as a plug-in into Eclipse 3.5.2 OS X 10.6.3