code: public void sort(Sorter sorter) {
          if (!(mWrappedRunner instanceof Sortable)) {
              return;
          }
          Sortable sortable = (Sortable) mWrappedRunner;
          sortable.sort(sorter);
      }
docs: IMPORTANT: We need the following method as the original Runner might
  implement the interface and we need to propagate the call. Note that this
  can get tricky if somebody checks for instanceof on the Runner (we would
  be out). Implementing this method was inspired by ant and
  "ant junit-single-test -Djunit.testcase=org.apache.tools.ant.taskdefs.optional.junit.JUnitTaskTest"
  that actually invokes filter to run only a single method.