Sunday, January 18, 2004

Bile for test-driven development

BileBlog has a strong rant against test-driven development. I see his point. Personally, I uses a hybrid of TDD and code-first development, depending on what suits my whim. More to the point:

The problem with the TDD crowd is that they're unwelcome guests in a world that doesn't want or care about them. I'm very sick of TDD bigots being snooty, getting offended, and angrily tugging at their unmentionables every time they see a unit test that doesn't meet their ludicrous standards for what constitutes a unit test.

So, let's look at a concrete example. I'd like to test a servlet. The servlet is standalone, it doesn't call anything else, it just Does Stuff. It's a standalone unit for all intents and purposes. There's no webwork, struts, or any such crap involved. I don't want it to be a wrapper with the work done in a POJO. I just want my single damn servlet. Sometimes a servlet is just a servlet.

The TDD asshats will now start furiously chewing on their desks if you try to use any sort of real container in your unit test. To them, that pollutes the test, you're in fact testing the container too and not just your servlet. That, astoundingly, makes it an invalid unit test (or at best, crippled, awkward, unwieldy).

Even more incredible are the suggestions they offer up to overcome this crippling (!) dependency. Suggestions that range from not using a servlet, to using mocks, to getting some POJO's involved, all so that you can have clean unpolluted tests.

To make some of my fellow ThoughtWorkers aghast, I have to agree here with the rant. And he, too, dances the hybrid dance:

I don't write my tests first. I know very few people who do. It's awkward, fragile and unintuitive. For those who enjoy it and find that it's none of those things, great! At best, I'll do a mixture of the two, and have something vaguely functional, then write a testcase and make sure it tests all the conditions I'd like it to pass under even though I know that it'll fail.

The most important thing is not to follow fashion, but do what works for you. Or just Do The Right Thing:

Two famous people, one from MIT and another from Berkeley (but working on Unix) once met to discuss operating system issues. The person from MIT was knowledgeable about ITS (the MIT AI Lab operating system) and had been reading the Unix sources. He was interested in how Unix solved the PC loser-ing problem. The PC loser-ing problem occurs when a user program invokes a system routine to perform a lengthy operation that might have significant state, such as IO buffers. If an interrupt occurs during the operation, the state of the user program must be saved. Because the invocation of the system routine is usually a single instruction, the PC of the user program does not adequately capture the state of the process. The system routine must either back out or press forward. The right thing is to back out and restore the user program PC to the instruction that invoked the system routine so that resumption of the user program after the interrupt, for example, re-enters the system routine. It is called PC loser-ing because the PC is being coerced into loser mode, where loser is the affectionate name for user at MIT.

The MIT guy did not see any code that handled this case and asked the New Jersey guy how the problem was handled. The New Jersey guy said that the Unix folks were aware of the problem, but the solution was for the system routine to always finish, but sometimes an error code would be returned that signaled that the system routine had failed to complete its action. A correct user program, then, had to check the error code to determine whether to simply try the system routine again. The MIT guy did not like this solution because it was not the right thing.

The New Jersey guy said that the Unix solution was right because the design philosophy of Unix was simplicity and that the right thing was too complex. Besides, programmers could easily insert this extra test and loop. The MIT guy pointed out that the implementation was simple but the interface to the functionality was complex. The New Jersey guy said that the right tradeoff has been selected in Unix -- namely, implementation simplicity was more important than interface simplicity.

The MIT guy then muttered that sometimes it takes a tough man to make a tender chicken, but the New Jersey guy didn’t understand (I’m not sure I do either).

Be a tough man. Or not.

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