Since IP is a fairly simple, self-contained, protocol it didn't require a large amount of testing. In order to test the IP block with PPP, it was possible to make a very small test harness, containing 2 IP and 2 PPP blocks, which sent chunks of data for IP to package up and send to PPP. PPP would then pass the data over to the mirroring PPP block which would send this data onto IP to 'receive'. It was possible to gauge the success or failure of the operation by simply attaching watchpoints to the input and output ports and manually examining the output of these points as the data was passed around.
In order to test the interoperation with TCP, IP was simply used in conjunction with the dummy application and TCP block as described in the TCP Testing section