Skip to main content

Unit Testing C# attributes

For a recent coding session I needed to handle an exception being thrown when some Json was incorrectly bound to a view model. With the framework we were using (ASP.NET MVC2) I was unable to handle the exception at the controller level, nor could I handle it at the "global" level when the framework carries out its bindings. Another way ASP.NET MVC handles exceptions is via attributes to catch errors you specify. The resulting exception is strongly typed and then can be passed into a view, from which you have full control of what to do. Typically we would log the error, display a friendly message and so forth.

In the past these attributes have been simply applied without a test - the general consensus being this was a framework specific thing which had no value in being tested. I agreed with those statements up until several minutes ago. Having fixed a defect in which the user was not seeing a friendly error message I carried on with a new feature only to find somehow the error handling had broken. It turned out I had indeed broken the attribute by providing an incorrect parameter.

As luck would have it there is a very nice, quick way to unit test attributes as discussed on StackOverflow. In the end I created several tests to check the following:

  • The type of the attribute is correct
  • The attributes properties were correctly set

The tests ended up ensuring that my action does indeed handle certain exceptions, redirecting the user to the correct view. The nice thing about these tests are they will only take minutes to write next time, yet save me a long time figuring out why the error handling has broken. Plus being unit tests they execute in the blink of an eye, no need to write a regression test to check the redirection has been carried out. These tests are therefore more "documentation" of how the system should behave.

Comments

Popular posts from this blog

Constant Object Anti Pattern

Most constants are used to remove magic numbers or variables that lack context. A classic example would be code littered with the number 7. What does this refer to exactly? If this was replaced with DaysInWeek or similar, much clarity is provided. You can determine that code performing offsets would be adding days, rather than a mysterious number seven.Sadly a common pattern which uses constants is the use of a single constant file or object. The beauty of constants is clarity, and the obvious fact such variables are fixed. When a constant container is used, constants are simply lumped together. These can grow in size and often become a dumping ground for all values within the application.A disadvantage of this pattern is the actual value is hidden. While a friendly variable name is great, there will come a time where you will want to know the actual value. This forces you to navigate, if only to peek at the value within the constant object. A solution is to simple perform a refactor …

Three Steps to Code Quality via TDD

Common complaints and problems that I've both encountered and hear other developers raise when it comes to the practice of Test Driven Development are: Impossible to refactor without all the tests breakingMinor changes require hours of changes to test codeTest setup is huge, slow to write and difficult to understandThe use of test doubles (mocks, stubs and fakes is confusing)Over the next three posts I will demonstrate three easy steps that can resolve the problems above. In turn this will allow developers to gain one of the benefits that TDD promises - the ability to refactor your code mercifully in order to improve code quality.StepsStop Making Everything PublicLimit the Amount of Dependencies you Use A Unit is Not Always a Method or ClassCode quality is a tricky subject and highly subjective, however if you follow the three guidelines above you should have the ability to radically change implementation details and therefore improve code quality when needed.

DRY vs DAMP in Tests

In the previous post I mentioned that duplication in tests is not always bad. Sometimes duplication becomes a problem. Tests can become large or virtually identically excluding a few lines. Changes to these tests can take a while and increase the maintenance overhead. At this point, DRY violations need to be resolved.SolutionsTest HelpersA common solution is to extract common functionality into setup methods or other helper utilities. While this will remove and reduce duplication this can make tests a bit harder to read as the test is now split amongst unrelated components. There is a limit to how useful such extractions can help as each test may need to do something slightly differently.DAMP - Descriptive and Meaningful PhrasesDescriptive and Meaningful Phrases is the alter ego of DRY. DAMP tests often use the builder pattern to construct the System Under Test. This allows calls to be chained in a fluent API style, similar to the Page Object Pattern. Internally the implementation wil…