private MachineConfiguration createMachineConfiguration(Collection<Class<?>> testClasses) {
   MachineConfiguration machineConfiguration = new MachineConfiguration();
   for (Class<?> testClass : testClasses) {
     GraphWalker annotation = testClass.getAnnotation(GraphWalker.class);
     if (isTestIncluded(annotation, testClass.getName())) {
       ContextConfiguration contextConfiguration = new ContextConfiguration();
       contextConfiguration.setTestClass(testClass);
       machineConfiguration.addContextConfiguration(contextConfiguration);
     }
   }
   return machineConfiguration;
 }