Dennis Burton's Develop Using .NET

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Tags: programming | tdd

RowTests are a great tool for consolidating tests that have the same logic, but differ by the parameters and the expected values. I did a post a while back on using RowTest in MbUnit, and Michael Eaton recently posted on using RowTest with NUnit. Reading Eaton's post reminded me that I had just run into a new feature in the NUnit 2.5 drop. One of my favorite features of competitive open source tools is that they usually add at least one feature more than the other guy with each release. For the 2.5 release of NUnit, one of those features is the ValuesAttribute. Granted, MbUnit had this feature in concept with CombinationalTestAttribute, but the usage of the ValuesAttribute in NUnit seems much cleaner to me.

Tests with no [Values]

Looking at the previous posts on RowTests, you can see that passing in many values for a specific test is not that difficult. So why would we need anything else? In certain scenarios, the number of permutations that you would have to write Row attributes for could be pretty cumbersome, and if it is truly a permutation scenario, difficult to maintain. The test case for this post will be that the test should be called with all possible combinations of 1,2,3 for one parameter and 10,20,30 for another parameter. With this simple example you can see that we have already blown up to 9 rows, adding on more variant onto either of the parameters and we would have 12 rows to maintain.

Giving your tests [Values]

What the values attribute does is allow you to express all 9 of these combinations in a very concise syntax. This lines up better with the expression of your requirements; instead of 9 Row attributes, you would now have the following:

public void Use_Value_Attributes([Values(1,2,3)] int param1,[Values(10,20,30)] int param2)
    r.DoStuffWithParms(param1, param2);

This nicely wraps up in one line what would have been expressed with 9 [Row] attributes in the past. Bring this up in the NUnit gui to verify that the tests you were looking for were in fact generated.


What do you use it for

Now that you have such a powerful tool in you toolset, start to think about how this would be useful. The real world case where I use this feature ensures that interaction with an external library is correct both in number and order of calls when the actual parameters from the system are applied. This test is purely focused on the behavior of the system not the expectation of a mathematical result.

What wouldn't you use it for

It would be very difficult to tie an expected value to the generated permutations. So if you are going after a specific output from an algorithm, a RowTest will work much better for you. Keep in mind that the RowTest feature has been around a while, so it is likely that you will use it more often.

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