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Unit Testing Gives Merit to Design Patterns

An entry about tdd | design patterns Publication date

8. December 2008 23:58

Son Hui has written a post in which he shows how using TypeMock helps him mock the SmtpClient class. At the beginning of his post, he writes:

“The proponents of TDD would like to use Dependency Injection(DI) technique to inject the SmtpClient dependencies into the mail sending class in order to facilitate unit testing.“

I would much rather say that the reason we do dependency injection is to achieve what is called the dependency inversion principle. I think this is one of the biggest misconceptions a lot of people have when faced with unit testing: the idea that in order to make code testable, they have to apply all of these academic design patterns. But, isn't´t just the fact that these design patterns makes code easier to test just more proof that they actually work?

Go SOLID today.

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Comments

12/14/2008 10:12:21 PM

We do a great disservice to the systemic improvements brought on by design when programmers use SOLID merely as a means of talking about making things "testable". Testability is a side-effect of SOLID, and we can get SOLID through TDD, but the whole point of SOLID isn't testability. Testability is only a concern to programmers, and then only to programmers who are already testability insiders. Equating SOLID with "testability" is only a meaningful conversation within the echo chamber, and once inside the echo chamber, it's likely not a necessary conversation.

The fact that these design patterns makes code easier to test is more proof that they actually work, but this is just a side effect of the more primary issue: these patterns make programming easier... period.

Of course, having more knowledge and fluency with any work will inevitably make it easier, but that's a proposition that won't sell itself either.

Scott Bellware

12/14/2008 10:37:48 PM

Scott, I wish your comment was my post - it says exactly what I was trying to say

Fredrik

1/5/2009 1:58:36 PM

We also make a great disservice to Automated testing when we mislead people to think that using SOLID is a must in order to test your code.

Adopting Automated testing (or TDD) is hard enough without us stacking more entry barriers like SOLID. I have seen too many companies showing AUT the door out, just because they got the notion that in order to start test their code they must first rewrite large parts of it.

As Scott said lets adopt design principles for the sake of better design and lets leave Testing consideration for testing principles.

I think that Son post is all about how by using a tool one can test any given design.

lior

1/12/2009 5:05:51 PM

@lior I disagree with the first thing you say - good design practices must come first, /then/ you can efficiently test your code. Thats not to say that you cannot test badly designed code - but it is vastly more difficult, and if you´re not a good enough developer to understand and apply good design principles then chances are you will not be able to do it well (or at all). Check out Jeremy D. Millers post on this - codebetter.com/.../design-and-testability.aspx - I completely agree with his point of view. Its a hotly debated issue though, as the comments on his post prove

Fredrik

Unit Testing Gives Merit to Design Patterns

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