Thursday, October 21, 2010

Test First

Test-First Teaching provides a fundamental shift in the way people learn software development. Initially, it helps the student focus on learning very basic syntax, able to independently confirm when they have successfully completed an exercise. That immediate feedback is valuable for cementing knowledge.

Test-first teaching also teaches an understanding of all of the arcane error messages in a low stress situation. The first thing you see, before you have written a line of code, is an error. Then you discover what you need to do to fix that error. Test-first teaching helps people intuitively understand that mistakes are a natural part of the software development process.

In traditional programming exercises, you are either given a fairly large task and asked to implement the whole thing, or you are provided with "skeleton code" -- source code that has been eviscerated to remove key sections, which you are asked to fill in.

"Large task" exercises are often challenging to students because of their sheer size. Many lines of code need to be written before you receive any positive reinforcement. This can be frustrating to beginners, and boring for advanced students.

"Skeleton code" exercises are also frustrating. The task of the student should be to figure out how to write code that will accomplish the given task. With skeleton code, you are first presented with the task of figuring out what the original author was trying to do; of reading through the code (often littered with idiosyncratic idioms and obscure comments); and then of trying to implement just one part of the algorithm, without necessarily understanding the larger picture. If the fill-in-the-blank code section is too complicated, the student may never complete the assignment; if it's too simple, no learning may be gained by the exercise.

Finally, in both types of traditional exercises, as a student you don't really know when you are finished! Sometimes, you will succeed in the task, but neglect to print the results, and will keep at it, believing you are still missing something; other times, you might write code that seems to work but is crucially flawed in some way or another. This is one of the most powerful features of test-first development -- you code until the test passes, and then you stop coding. The test provides a map, informing you of where to begin, and where to end.

Test-first teaching is appropriate for both guided and solo use. Students in a classroom may rely on classmates or teachers for guidance; but if alone, the tests provide some measure of feedback and guidance (although unit tests can never actually debug and fix the code).

Perhaps the most important aspect of test-first teaching is that it teaches the whole process, from opening a new file in a text editor to compiling and running. At the end of the day, the students can say, "At least I know how to write a program." Many exercises, especially skeletons but also those based on tools and toy problems, end up skipping the fundamentals that are vital not just for coding on a day-to-day basis, but also for cementing the higher-level concepts into habits and skills.

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