Cost of Testing
Now, I think that if you look at these two chunks of code, it is easy to see that even though they are about the same length, one is much harder to write. The reason, why tests take so little time to write is that they are linear in nature. No loops, ifs or interdependencies with other tests. Production code is a different story, I have to create complex ifs, loops and have to make sure that the implementation works not just for one test, but all test. This is why it takes you so much longer to write production than test code. In this particular case, I remember rewriting this function three times, before I got it to work as expected.
He then explains what the 10% cost of tests buys him.
