Bug 41798 New JUnit Plug-in test requires test suites to extend Test
The new JUnit plug-in test seems to require test suites to extend TestSuite. Otherwise an error is reported in the launch config dialog. It is however still possible to launch a test suite by opening it in the editor and choosing Run->Run As->New JUnit Plug-in Test To reproduce, try to run (and configure) the JDT UI AllAllTests testsuite.
org.eclipse.jdt.junit.core/src/org/eclipse/jdt/internal/junit/util/TestSearchEngine.java
!Flags.isPublic(method.getFlags()) ||			
			!Flags.isPublic(method.getDeclaringType().getFlags())) { 
			return false;
		}
		return true;
	}
	
	private static boolean isTestType(IType type) throws JavaModelException {
		if (Flags.isAbstract(type.getFlags())) 
			return false;
		if (!Flags.isPublic(type.getFlags())) 
			return false;
		
		IType[] interfaces= type.newSupertypeHierarchy(null).getAllSuperInterfaces(type);
		for (int i= 0; i < interfaces.length; i++)
			if(interfaces[i].getFullyQualifiedName().equals(JUnitPlugin.TEST_INTERFACE_NAME))
				return true;
		return false;
	}
	public static boolean isTestImplementor(IType type) throws JavaModelException {
		ITypeHierarchy typeHier= type.newSupertypeHierarchy(null);
		IType[] superInterfaces= typeHier.getAllInterfaces();
		for (int i= 0; i < superInterfaces.length; i++) {
			if (superInterfaces[i].getFullyQualifiedName().equals(JUnitPlugin.TEST_INTERFACE_NAME))
				return true;
		}
		return false;
	}
}