I originally wrote this post back in November 2009 over at my old blog at geekswithblogs.net. Because it still receives some hits, I decided to take it with me and copied it to my new blog. With the exception of some necessary HTML polishing, this article is unchanged compared to its previous version.
The Gallio testing framework (which essentially is MbUnit) that I was using at this time, is no longer available. But it’s very similar to NUnit and you can easily read the code samples if you’re familiar with NUnit. I updated the accompanying sample solution to use NUnit (but not the code excerpts in this post). Also, I updated it to VS 2013 and NuGet and gave it a new home on Github.)
One of the single most influential cost factors for software projects is code readability and understandability – and the most important factor for readability in turn lies in the adherence to Coding Style Guidelines. To enforce such guidelines, Microsoft has provided a free tool which checks a given set of source code files against a given set of style and consistency rules: MS StyleCop. The tool comes with quite a lot of predefined rules – however, they mirror the coding practice at MS and not all of them may be appropriate or sufficient for others. Therefore, StyleCop allows for authoring custom rules to extend or modify the original set of rules. How this can be done, is well covered elsewhere on the web (e.g. here, here, or here).
But in contrary to the rules authoring issue, very little – almost nothing – can be found that deals with testing issues. All I found was this post, which gave me a first insight into the issue and inspired me to write a custom Gallio/MbUnit test fixture that lets you write tests against StyleCop rules as simple as this:
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[Test, TestsOn("SA1200: UsingDirectivesMustBePlacedWithinNamespace")] public void TestUsingDirectivesMustBePlacedWithinNamespace() { AddSourceFile("../../TestFiles/UsingDirectiveOnTop.Testfile.cs"); RunAnalysis(); AssertViolated("UsingDirectivesMustBePlacedWithinNamespace"); } |
Alternatively, you may check if a certain rule was violated for the expected number of times…
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AssertViolated(3, "UsingDirectivesMustBePlacedWithinNamespace"); |
..or at the expected line numbers…
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AssertViolated("UsingDirectivesMustBePlacedWithinNamespace", 1, 2, 3); |
…or you may check against a caller-provided predicate function….
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AssertViolated(@violation => @violation.Rule.CheckId == "SA1200"); |
…and if none of the above options fits your needs, you may directly access the generated violations and/or the generated text output:
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Assert.AreEqual(3, Violations.Count); Assert.AreEqual(2, Output.Count); |
If such a test fails, then you might find something similar to this in the test report:
To make this work, the containing test fixture derives from a base class called StyleCopFixtureBase. This class takes care of setting up the StyleCop engine, (silently) running it against the specified files, capturing the resulting violations together with the generated console output, and cleaning up after each test run. It also provides the necessary methods and properties for adding files and additional addin path, and also some specialized assertion methods. To test a rule, you only have to specify the file(s) that you want to test, run the analysis, and then check the results. This is not only shamefully simple and easy to use (i.e. to write) – such unit tests are also a pleasure to read, in that they tell the reader clearly and unambiguously what they are doing…
In the usual use case scenario (the assembly with the rule(s) under test can be found in the calling assemblies’ bin directory, together with the StyleCop assemblies), you only have to provide a StyleCop.Settings file [*] with your test project, which must be copied to the bin folder (i.e. the Copy to Output Directory property must be set to Copy always or Copy if newer), and you’re done. If necessary, however, the StyleCopFixtureBase class also allows for eventually required path adjustments. I won’t go further into details here – you can get the StyleCopFixtureBase class from the this Github repository and then refer to the class’ documentation, which is pretty detailed.
* Tip: You can copy the settings file from the StyleCop install directory and then edit it as required…
The sample solution
A small sample solution (VS 2013) can be downloaded from here. It contains the StyleCopFixtureBase class along with detailed xml documentation and some basic usage examples.