"Here's a binary search algo description, implement it perfectly without testing".
That's not even close to how developers work, and he amplifies the disconnect with the real world by choosing a problem known for it's boundary and off-by-one risks.
Also: no amount of test-drivenness can save you from just not grokking the problem (as Peter Norvig's Sudoku solver showed ... er, by counter-example.)
The code will behave incorrectly on some edge cases, but if the developers and QA have covered the problem domain pretty well, it won't matter. First, most of the edge cases will never happen. Second, people get angry when software fails for no obvious reason, but they tend to be a lot more forgiving when software fails on inputs that are "freakish" or "wrong" in the domain context. Searching the widget catalog results in "500 Internal server error" when the widget catalog is empty? Well, duh! When should the widget catalog ever be empty?! The search page shows screwy results because someone entered an item with a negative price? Well, duh! Get that stupid item out of the catalog! Instead of thinking like a mathematician or a system designer in order to avoid mistakes, the typical development approach is to think like the customer so you only make mistakes that the customer can sympathize with.
I would also point out that for a lot of programming tasks, particularly in a corporate IT environment, "thinking like the customer" can be a good thing: it helps you make sure that you are building something that truly helps the customer do their job.
The risk is that no matter how much "domain experience" you have, the customer has more, and you can fool yourself into thinking that you understand what they need better than they do.
The fact that it's tractable to rigorously consider all the edge cases means it is ridiculously simple compared to common real-world programming tasks.
You'd be surprised. Also, terrified.
So, one of the assignments was to write a program, and desk check it until you were confident that it would compile and run correctly on the first try. It was a one-chance, pass/fail assignment: it either worked, or there was a compile or runtime error.
Maybe in the "real world", the programming is just the simple gluing together of hard stuff like databases, compilers and operating system, since they have already been written. Once you have some bullet-proof method, it really is better to just be a consumer of it.
There is still some hard stuff that needs to be done, though. I suspect that to do "the hard stuff" you need to be able to implement simple-but-serious algorithms in a few lines. This makes your overall code smaller, more readable and allows optimization for the particular cases you're working with.
I don't think the parent was objecting to implementing a simple but serious algorithm in a few lines, but to doing so without performing any testing at all.
There is still some hard stuff that needs to be done, though.
Yes, and I'm pretty sure the people doing that hard stuff do some testing ;)
raganwald says, "It feels very retrograde to try to write the whole thing out and only then start thinking about [...] edge cases." Nobody said you had to write it before thinking about edge cases! The idea is to think about the edge cases and incorporate that thinking into the code before you actually test the code--whether you can be--actually whether you know the steps to be--that thorough in your head.
One way to think about edge cases, of course, is to write the test code before the function. But after writing the tests, try writing the function correctly before testing it.
Of course, one of the potential bugs in binary search doesn't occur to people before they write and then try it. And, that bug is hard to test for, ahem, don't want to explain why.