Testing the internet (or how to mock a web service)

Part of the architecture of project Awesome involves an engine that processes a high number of tasks, each requiring a significant amount of work. While I can't explain what the engines main responsibility is, this is related to the persistent queue I mentioned in a previous post.

At the end of each unit of work, a message is sent to an external system for additional work to be done. However, because the external system is essentially a non-blocking remote queue, we get no feedback or information about the state of the work being done. To solve this, there is yet another service which returns feedback on the process of each unit of work as it executes on the remote system. We reconcile the feedback with each unit of work sent for processing.

Because there are so many steps involved, testing this entire process is a bitch. Testing this entire process in Fitnesse is even harder. The engine spans threads to periodically check the incoming queue and poll the feedback service. Since Fitnesse runs in a single thread, we will need to test some of the threading issues with JMeter (for example, if two callers attempt to place the same item in the queue, only one should be accepted). However, we don't have the resources to do JMeter, so for now, we'll have to hope that our unit tests are enough.

So, the external system gets mocked in Fitnesse! To accomplish this, we create an actual HTTP server on the local system which we can control within test tables. Fitnesse starts up this mockable server, and then starts the engine, telling it to call the address of our mocked service. With no changes to it's existing code, our engine is now processing records that we can include directly from our wiki.

While this doesn't test the entire engine, it does allow us to test one critical piece. We can now verify our engine performs correctly, regardless of the state of actions of the external service (in fact, we can even make it do things it shouldn't ever do - just in case).