code: @Override
      public SingleInspectionSpecifier observe(Class<? extends RequestObserver> what) {
          initializeSingleGroup();
          singleGroup.observe(createFilterInstance(what));
          return this;
      }
docs: /*
  (non-Javadoc)
  @see org.jboss.arquillian.warp.client.execution.FilterSpecifier#filter(java.lang.Class)