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MBUnit to NUnit

Over the last few weeks we've ported our tests from MBUnit to NUnit. This was done as after a quick spike it was seen that NUnit tests run almost fifty percent quicker. For example our common projects' test time went from around 40s to around 20s on average.

This whole process was no easy task. Initially our largest project was converted by the whole team. We split into pairs/individuals and tackled a test project each. Working in this manner we could commit after each project, meaning at any one time the build was only fractionally broke, rather than completely unbuildable. Previously we tried a big bang approach but after several thousand errors, we quickly reverted. After each commit the tests were gradually moved over. This took around an hour or so, and therefore our allocated dojo/technical dojo time for that week was used. For the remaining projects an ad-hoc approach was taken. The first pairs to work on a project would be responsible for porting the tests over. Thankfull our other projects bar one were fairly straightforward to upgrade and were done as part of waste or kaizen.

Some of this process could be automated however things were not completely smooth. For example converting the MBUnit namespace over was achieved by project level find and replace. Other issues such as Asserts being slightly different required a manual fix. One example being asserting a exception is thrown. The MBUnit approach used attributes while in NUnit it is more preferable to use Assert.Throws. The other issue we faced was porting over the relevant build scripts and Cruise Control configs. Again there was no easy way to do this. We had a fair few CI fails when this was done, but when editing the xml build files there is no real way to test what you've done without actual trying it!

Overall the whole episode was not as bad as I thought it would be. We seem pretty stable at time of writing, and the tests are definitely quicker to run locally. We still have slow tests, and as part of waste we'll be looking into whether these slow tests are needed. One interesting practice I've noticed over the upgrade is how many dodgy tests we've removed. Tests such as Assert.IsNotNull after creating a new object - the sort of tests everyone writes when starting TDD have been removed. These legacy tests serve no purpose now, but were the key starting point of the TDD introduction to Codeweavers several years ago. Other tests which are covered else where or simply not needed were also removed. The final issue we are aiming to improve is that of our regression/acceptance tests, many of which are Selenium tests.

Would we recommend upgrading your test suite to the latest/next best thing? Not unless you can prove with figures that it has an actual benefit. We provided no value to the business by doing this, but by hopefully taking one step to increase our feedback cycle we'll see the benefit over time. If anything, we should be more likely to run our tests. As for why MBUnit was slower? It features a lot of stuff we simply don't need, while NUnit is more lightweight and just plain faster for our use. We could perhaps speed the tests even more by writing our own test runner, but the likes of Visual Studio integration are a must therefore this is no easy task.

One interesting point to conclude was that during this process there was talk about wrapping NUnit within a Codeweavers test framework, essentially meaning we could switch test frameworks whenever. Is this overkill for most projects? Most likely, but it was something to consider especially for large applications. As who knows, maybe there will be an even faster framework out there that we can upgrade to again, next year...


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