CODEWITHSUNDEEP
unit-testingmstest
scubasteve
scubasteve

Reputation: 2858

Strategy to simulate events in object under test

BRAND NEW to unit testing, I mean really new. I've read quite a bit and am moving slowly, trying to follow best practices as I go. I'm using MS-Test in Visual Studio 2010.

I have come up against a requirement that I'm not quite sure how to proceed on. I'm working on a component that's responsible for interacting with external hardware. There are a few more developers on this project and they don't have access to the hardware so I've implemented a "dummy" or simulated implementation of the component and moved as much shared logic up into a base class as possible.

Now this works fine as far as allowing them to compile and run the code, but it's not terrible useful for simulating the events and internal state changes needed for my unit tests (don't forget I'm new to testing)

For example, there are a couple events on the component that I want to test, however I need them to be invoked in order to test them. Normally to raise the event I would push a button on the hardware or shunt two terminals, but in the simulated object (obviously) I can't do that.

There are two concerns/requirements that I have:

  1. I need to provide state changes and raise events for my unit tests
  2. I need to provide state changes and raise events for my team to test dependencies on the component (e.g. a button on a WPF view becomes enabled when a certain hardware event occurs)

For the latter I thought about some complicated control panel dialog that would let me trigger events and generally simulate hardware operation and user interaction. This is complicated as it requires a component with no message pump to provide a window with controls. Stinky. Or another approach could be to implement the simulated component to take a "StateInfo" object that I could use to change the internals of the object.

This can't be a new problem, I'm sure many of you have had to do something similar to this and I'm just wondering what patterns or strategies you've used to accomplish this. I know I can access private fields with a n accessor, but this doesn't really provide an interactive (in the case of runtime simulation) changes.

Upvotes: 2

Views: 431

Answers (1)

Richard Banks
Richard Banks

Reputation: 12546

If there is an interface on the library you use to interact with the external hardware you can just create a mock object for it and raise events from that in your unit tests.

If there isn't, then you'll need to wrap the hardware calls in a wrapper class so you mock it and provide the behaviours you want in your test.

For examples of how to raise events from mock objects have a look at Mocking Comparison - Raising Events

I hope that helps!

Upvotes: 2

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