A test group is basically just a facade for the test class.

TestGroup.cs

namespace Mjunit
{
    class TestGroup : IEnumerable
    {
        private readonly Type _testClass;
        private readonly ArrayList _testMethods = new ArrayList();

        public TestGroup(Type testClass)
        {
            _testClass = testClass;
            var methods = _testClass.GetMethods();
            for (int i = 0; i < methods.Length; i++)
            {
                var m = methods[i];
                if (m.Name.Substring(0, 4) == "Test" && 
                    m.ReturnType == typeof(void))
                {
                    _testMethods.Add(m);
                }
            }
        }

        public Type TestClass
        {
            get { return _testClass; }
        }

        public int NumberOfTests
        {
            get { return _testMethods.Count; }
        }

        public IEnumerator GetEnumerator()
        {
            return _testMethods.GetEnumerator();
        }
    }
}