Last week, Alex Knapp, a general technology blogger for, ran a short article on model-based testing.

I took a fair bit of issue with the article, and called him on it. I must say, I was impressed with Alex’s response.

First, he followed up his summary post with an interview with a little more depth. Second, the guy called me to dialogue, in a friendly way.

I’m still not impressed with the original piece, and have issues with the interview. What impressed me was the follow-up, the genuine interest to figure out the truth, the willingness to consider both sides of the discussion. As a general-interest “tech” blogger, Mr. Knapp didn’t have a deep understanding of testing when he began the process … but I have the impression he might when he finishes.

Anyway, after posting the interview, he asked me for my feedback, and I gave it over email. Afterwords, we kept talking, and thought it might be worth sharing with, well, everybody else. So here goes … my reply to the latest interview:

As a tester, I run into this idea all the time — that we can automate away testing. It seems like every year, a new crop of students graduats from CMU, Berkely, and MIT with CS degrees. (Only thing is: They haven’t studied testing.)

What computer scientists do, of course, is write programs to automate business processes. So it makes sense that someone with a CS degree would say “hey, testing, there’s a straightforward business process — we should automate it!”

I do want to give Mr. Bijl’s some credit for this strategy — model-based testing is a more complete, more cost-effective way to test applications than traditional, “linear” test automation.

It’s also not new — Harry Robinson has been championing the idea for going on a decade. You might even check out his website — Harry has worked at Google, Microsoft, AT&T. He is currently BACK at microsoft on the bing team. Really good guy.

What impresses me about Harry is that he is realistic in what model-driven testing can do.

For example, let’s look at Mr. Bijl’s rhetoric one more time:

“It enables to automate all phases of software testing: test creation, test execution, and validation of test outcome.”

If that were true, then he would basically develop a BUTTON, right? You’d type in a URL and click “test it” and then get test results.

Of course, this can’t possibly work. Sure, you could write software to go the URL, look for input fields, type in random inputs and click random buttons. You could get back 404 errors from broken links and such, but, most importantly, the tester software wouldn’t know what the tested software should do, so it would have no way to evaluate correctness. Whether it’s a simple Fahrenheit-to-Celsius converter or, either way, you need to embed business rules into the test program to predict what the right answer is, and to compare the given answer to “correct.”

In software testing, we call this the “Oracle” problem.

That “oracle” is the “model” in model-based testing. Someone still has to program it.

Once you “just” program the model, then you can set your application free on the website, to bounce around, sending valid input and looking for errors.

The problem is that little term “just.” It turns out that, in most cases, programming a model is exceedingly complex. (Google “The unbearable lightness of model based testing”.) Oh, I’ve done a fair bit of it — for example, if you have some complex business rules in a database, and need to predict an “answer” to a question for a given userID, you might have two programmers code the application, then compare results with a FOR loop. I have done this.

For more complex applications, especially ones with a GUI, the number of states to transition begins to grow exponentially. Most people applying MBT generally “give up” and use it find errors, because errors codes are easy to predict. The problem being, this doesn’t tell you on cases where no error is generated but the business logic is incorrect.

I don’t mean to be too critical of MBT — it’s a good tool for your toolbox. Presenting it as the solution to all testing woes, well, yes, I take issue with that. If you’d like to do an interview with Forbes, or moderate a point-counterpoint or such, I’d be interested in it. (I know you are a generalist, maybe Forbes could use a test/dev specialist blogger?)

I’ll be at the Conference for the Association for Software Testing (CAST 2011) in August in Seattle, and the Software Test Professionals Conference (STPCon 2011) in October in Dallas. I’m happy to talk more about this.

Here we have an interesting topic, a receptive audience, and the capability to cause a little bit of change. I don’t know about you, but I a more than a little tired to the every-batch-of-CS-grads-sees-testing-as-something-to-code-up mentality.

I took a shot. The audience seems receptive; I even proposed a point-counterpoint interview as a next step. Does anyone else have an idea on how to keep the ball rolling?