Integration Testing, part 5 More than one test may be needed

In my last post I mentioned a test that we can run on the specifications for the engine and muffler.  This is notionally a check we write a script for the computer to run and validate that the components will work with each other.

That is probably not enough, though.  Just checking the data sheets is no guarantee the actual muffler and engine will work together.  Imagine a scenario in which the redline (the top speed) of the engine is given.  Then imagine that, for whatever reason, the engine we are using exceeds that speed.  In this case, the engine will start to output more exhaust than the ratings sheet indicates and our muffler may not be able to handle that much extra, unexpected exhaust.

One possibility for this is an emergency.  Suppose the driver needs to get to a hospital and doesn't care about the damage the car may take.  In this case, we need to verify the behavior of the engine + muffler even when it goes out of specification.

The testing here is mechanical in nature.  We create a fake engine of some sort that outputs more than we expect the real engine to produce and test with the muffler.  At this point, we document the behavior of the muffler.  Some reasonable expectations are:

1. The muffler fails immediately and simply does not process the exhaust.  Instead, it simply passes through with no catalytic converter and no sound reduction.
2. The muffler fails more catastrophically.  It could break, overheat or worse, even explode.
3. There is also a case that the muffler designers built a safety margin into their specification and did not document it.  In this case, the muffler may work, perhaps only for a short duration.

We don't know what we should do if the muffler + engine do not work together in this scenario.  At this point, the testing organization is in exploratory testing mode and simply needs to determine the behavior.  Once we have a clear understanding of what is likely to occur we can apply that knowledge to making a decision. 

I'll cover that next.

Questions, comments, concerns and criticisms always welcome,

John