Mark Needham

Thoughts on Software Development

TDD: Suffering from testing last

with 3 comments

I’ve always been a big proponent of writing tests before writing code, and I roll off the standard reasons to people who question this approach:

  • They help to drive the design
  • They provide a safety net when making future changes
  • They provide a way of communicating the intent of the code to the rest of the team

And so on. Despite knowing all this I recently took a non test driven approach to writing some bits of code – we were keen to get the system working end to end so it seemed a trade off worth making to prove that it was doable.

I knew that I would suffer when it came to testing this code after I had already written it and indeed it did!

I’ve tested around legacy code before and although Michael Feather’s book makes it much easier, it’s still not a great experience. The saving grace has always been that I didn’t write the code whereas in this case it was quite definitely my fault that I ended up with this problem.

The original pain came from not knowing where I should start. Since we didn’t have any tests I wasn’t sure exactly what the code was doing despite the fact that I had written most of it fairly recently.

In particular I ran into the problem whereby I wrote a test which passed so all seemed good. Suspicious as to whether this was the case I decided to comment out some of the code which was apparently making the code pass. I expected the test to fail and give me the red bar but in actual fact the test still passed!

It turned out that I had written the expectations for my mocks slightly wrong in the test – a mistake that I would have definitely caught if I had written the test first but could have easily missed by testing last.

After this I decided that because there wasn’t too much complex logic in this particular piece it would be much better to comment out the code and then test first before fitting it back together again. Eventually I got all the code covered but it took much longer than if I had just tested it properly the first time around.

For me software development is all about creating quick feedback loops and I find it very frustrating when I’m unable to do this. Testing first is one very good way of achieving this as it provides a clear way forward and gives feedback on our progress.

I will certainly be very reluctant to test last again.

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Written by Mark Needham

November 28th, 2008 at 12:34 am

Posted in Testing

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