I'm a huge fan of unit testing, but still make use of a FGDB to grab features for running unit tests against when using the ArcObjects framework.

Is anyone successfully using mocking against thinks like IFeature, IGeometry, IWorkspace etc. If so, I'd love to see some examples of how you're doing it. I don't really care about what mocking framework you use, just seeing how you're doing it would be greatly appreciated.

The problem I see is that you're having to slice and dice between so many interfaces on the same object, that the overhead of creating a representative mock object would be huge.


2 Answers 2


We have, on a large project, managed quite well to isolate ArcObjects code from our business logic. That is generally the way to go, I'd say, rather than attempting to mock it all out, even if it is possible using mocking frameworks to get some of the way.

Ask yourself, Why it is you feel the need to mock. Typically, it is because of a missing abstraction. Think small responsibilities and minimize the surface of the huge, ugly ArcObject monster. Avoid dragging around ArcObject types just because some aspect of them is needed somewhere.

I can give one concrete example from our project. A portion of the code seemed to depend on IMxDocument. It turned out the only reason was that the active view needed to be refreshed. So we created an IViewRefresher interface instead and only worked on that; easy to mock and test. Additionally, it makes the intent of the code much clearer and removes the temptation for someone to start doing funny things with the IMxDocument that they weren't supposed to do because all we wanted to do here was refresh. The same exercise can be done with a lot of the ArcObjects code.

Also, we wrapped all access to feature classes in type safe wrappers, again providing mockable code shielding the business code from ArcObjects.

We've discussed not even using the geometry types of ArcObjects, but currently we do allow those interfaces to be used directly in our code. (However, interface knowledge only is allowed and all instantiations of geometries use our own geometry factory.)

In summary, I'm not disencouraging mocking but I'd encourage mocking at a different level of abstraction than ArcObjects.

  • great answer Cumbayah. I also have a lot of dificulties unit testing AO code. The example you gave was great (IViewRefresher) and I might apply that to my work here. Can you give further examples? Commented Aug 23, 2010 at 15:43
  • Thanks Cumbayah. This is what I currently do on medium to large projects, creating a separate assembly to abstract all AO implementation. It's this abstraction I'd like to test without resorting to stored data though, be it XML workspaces or geodatabases of one sort or another. I find that from time to time with different data, new issues crop up, which then need to have tests created for, which necessitates additional test data. Over time I have so much test data for all test cases, that the projects become huge to manage and move around, let along download by my automated build server.
    – BlinkyBill
    Commented Aug 24, 2010 at 3:45
  • Cumbayah, this sounds incredible. I would love to some examples. Have you ever considered presenting something on this subject at one of the ESRI conferences? I think the ESRI/GIS community is dying for this kind of stuff. Would love to see some open source movement get started for testing/mocking ArcObjects.
    – Keith G
    Commented Dec 17, 2010 at 19:16
  • This is an old topic I understand, but any chance we can get a sample of your "own geometry factory"? I'm trying to get my organization moved in the direction of unit testing, but I'm getting hung up on the ArcObjects monkey.
    – Luke
    Commented Jul 30, 2012 at 15:08

Unit Testing for Esri Developers by Dave Bouwman and Brian Noyle is a pretty good starting place - particularly since they threw out some code to look at.

  • Thanks for the pointer bwreilly. What Dave does though is simply use XML representations of features. So while it's helping, it still relies on storing data for tests, which is what I'm trying to get away from.
    – BlinkyBill
    Commented Aug 24, 2010 at 3:47

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