anchor.diff:              case get(first_tested) of
                   undefined ->
                       put(first_tested, true),
  -                    meck:passthrough([undefined, Message]);
  +                    meck:passthrough([error, Message]);
                   _ ->
                       meck:passthrough([Stream, Message])
   
  
positive.code:             case get(first_tested) of
                  undefined ->
                      put(first_tested, true),
                      meck:passthrough([undefined, Message]);
                  _ ->
                      meck:passthrough([Stream, Message])
  
  
negative.code:             case get(first_tested) of
                  undefined ->
                      put(first_tested, true),
                      meck:passthrough([error, Message]);
                  _ ->
                      meck:passthrough([Stream, Message])
  
  