Mocking External Services

Should your tests mock outside services or not? I keep seeing discussions on this topic. On the one hand, it lets your tests be in control of the testing context. Otherwise it may be very difficult to create a reliable automated test.

  • The external service might return different results at different times.
  • The external service might be slow to respond.
  • Using the external service might require running the test in a particular environment.
  • It may be impossible to generate certain error conditions with the real service.
  • There may be side-effects of using the real service.

On the other hand, our mock of the external service might differ from it in important ways.

  • Our mock service might have a slightly different interface than the real one.
  • Our mock service might accept slightly different parameters than the real one.
  • Our mock service might return slightly different results than the real one.
  • The real service might change behavior, and we won’t notice until we deploy to production.

This leaves us in a quandary. What to do? (Continued)

An open letter about unit tests

An open letter to a programmer who thinks that code coverage by integration tests eliminates the need for unit tests. (Continued)

Pair Programming Lessons from Improv

Thanks to Tim Ottinger for reminding me of Arlo Belshee’s post, “Is Pair Programming for Me?” Go read Arlo’s post, as it’s insightful and has more useful content than most articles on pairing. I’m just going to springboard off of one skill that Arlo mentioned being important to learn.

How to avoid “paragraphing” when talking. Learning to speak in half-sentences, leaving room for the other to take the idea in an unexpected direction.

A few years back, I took a course in “Beginning Improv Acting.” (Continued)

Another Approach to the Diamond Kata

I saw that Alistair Cockburn had written a post about Seb Rose’s post on the Diamond Kata. I only read the beginning of both of those because I recognized the problem that Seb described with the “Gorilla” approach that, upon reaching the ‘C’ case.

“The code is now screaming for us to refactor it, but to keep all the tests passing most people try to solve the entire problem at once. That’s hard, because we’ll need to cope with multiple lines, varying indentation, and repeated characters with a varying number of spaces between them.”

I’ve run into such situations before, and it’s always be a clue for me to back up and work in smaller steps. Seb describes that the ‘B’ case, “easy enough to get this to pass by hardcoding the result.” Alistair describes the strategy as “shuffle around a bit” for the ‘B’ case. I’m not sure what “shuffling around a bit” means and I don’t think it would be particularly easy to get both ‘A’ and ‘B’ cases working with constants and not heading down a silly “if (letter == 'A') … elseif (letter == 'B') …” implementation. I was curious how I would approach it, and decided to try. (Ron Jeffries also wrote a post on the topic.) I didn’t read any of these three solutions before implementing my own, just so I could see what I would do. (Continued)

Why I Practice TDD

I was reading Laurent Bossavit’s book, “The Leprechauns of Software Engineering—How folklore turns into fact and what to do about it,” and came across his mention of “Comparing the Defect Reduction Benefits of Code Inspection and Test-Driven Development” by Jerod W. Wilkerson, Jay F. Nunamaker, & Rick Mercer. This struck me as an odd thing to study. Not only is Test-Driven Development not primarily about defect reduction, but the populations of defects it might reduce are likely to be very different from population of defects reduced by code inspection.

I then took a look at my own list of TDD studies and noted that most of these studies were focused on external quality as measured by absence of known defects, and time it took to develop the functionality. Keith Braithwaite, at Agile 2007, reported on internal quality, specifically Cyclomatic Complexity.

Quality and productivity are, of course, important things. And they’re easy to sell to some managers. Who could be against them? And I certainly wouldn’t continue to practice Test-Driven Development if it added defects or took a significantly longer time to create functionality. But that’s not why I practice TDD. (Continued)


Red-Green-Refactor Test Driven Development hatI’ve achieved some notoriety with my Test Driven Development hat. Not so much when I wear itat AgileTechDC2011, but certainly when Uncle Bob does. So much so that he has received queries about acquiring or making them. (Continued)

Rough Cut

A common complaint against Test Driven Development is that writing tests and refactoring take too long. In the long run, I’ve found that TDD has improved my skills such that I can complete work faster by writing tests and refactoring than without. I’ve also found that this information is a weak argument for those who have less confidence in their skills, or feel too pressed for time to learn. But that’s not the only benefit. (Continued)

Avoiding Mini-Waterfalls

A lot of people and organizations, when transitioning from a serial software development lifecycle toward an Agile one, fall into the pattern of mini-waterfalls. They start doing iterations, but each iteration resembles the development lifecycle they already know. The programmers do some design work, then they write the code to implement the design, then unit test the code, and then they pass it to the testers for testing. To many people, this is the only way it can work. Their mental model only admits to this series of phases.

And they run into typical problems. Sometimes the design doesn’t fit the problem well, and patches are needed because there isn’t time to go back to design. The testers get squeezed for time at the end of the iteration, and no one knows how to accommodate the rework when a problem is found. More patches are added, because there isn’t time to redesign. And the next iteration starts the cycle over again.

Sure, doing this in two to four week cycles beats doing it in six to twelve month cycles. But only a little. Most of the time, it starts to fall apart if the team doesn’t learn to work differently.

But it’s inevitable, they say. (Continued)

I feel better, now

Oops! The whole problem started when I wanted to install a new program on the “entertainment computer” that’s connected to the TV. The existing version of Ubuntu was no longer supported, so I started what I thought would be a simple upgrade. Oops, it deleted the entire /var directory, including the contents of the second drive mounted there. That drive contained all of our photos and music. Not a problem, I thought. It’s all backed up nightly onto a USB drive. It’s just a bit of bother to copy all of that over the USB interface.

Oops! There are no photos beyond last March. I felt sick to my stomach. That’s a lot of family memories to evaporated. Whew! The program we’ve been using to download the cameras also makes a backup copy local to the machine used to download. I’ve got all the pictures back on the photo server, and now just have to sort them into directories again.

But first, I need to fix the backup script. Why didn’t it warn me when it started to fail? (Continued)

Tips and Advice: Test Driven Development

Yesterday, Bob Payne published one of our informal Tips and Advice discussions on the Agile Toolkit. Check out our Test Driven Development podcast and let me know what you think.