Writing all these tests I sometimes felt that the changes between two days was not significant. And sometimes I felt there were versions that did not make it into this advent calendar. But I stuck with the versions you have seen since I think they represent a quite natural evolution of the initial test and hence I have not presented any side tracks that eventually turn into a dead end because I wanted to progress toward the final version which is the one I like most of all these versions. Also I had to be a little bit puristic and let even the smallest changes result in a version by it self rather than merging a number of small changes into a single version change in order get 24 different versions. There are however a few of the versions that I think are worth a special mentioning.

• December 3rd: I think this is a typical example of how people write their tests when they're starting out to use TDD. In my experience TDD novices tend to put too much into each test.
• December 5th: The second most common mistake is to forget that standard software engineering practices and common sense still apply to the test code. They tend to forget code reuse in their tests.
• December 11th: I think this is the first acceptable version in this series. Simple, easy to understand tests with code reuse. TDD novices that take TDD seriously typically end up with this kind of tests pretty soon.
• December 15th: The use of an object that extends the object under test and adds functionality needed to simplify testing is a great step forward toward writing good tests (IMHO). I think this version of the test basically is the first peek at BDD-type test-writing.
• December 20th: Now we have easy to understand tests and each method have really descriptive names that are easy to read. I think this is the first really good version of the test in this series.
• December 24th: In my experience people tend to put many different kinds of tests into the same test class ending up with tear-down code that has to take take the state of several tests into account. This makes the test class more complex than it has to be. The use of several specialized test classes for different types of test scenarios is definitely something you start thinking of after writing several unit tests. I think it is a common misconception that you should have one test class for each production class. Some test classes will test several production classes while others production classes will need several test classes to complete the test suite.

Please leave a comment and let me know what your favorite version in this series of test is!