code: public static Matcher<Class<?>> subclassOf(final Class<?> klazz) {
      return new Matcher<Class<?>>() {
  
        @Override
        protected boolean matchesSafely(Class<?> t) {
          return klazz.isAssignableFrom(t);
        }
  
        @Override
        public String toString() {
          return "a subtype of " + klazz;
        }
      };
    }
docs: Returns a matcher that matches classes that are sub-types of the  supplied
  class.
  
  @param klazz a potential super-type
  @return a {@code Class<?>} matcher