Keith Devens .com - Weblog: Unit testing in PHP

Friday, May 9, 2003

Unit testing in PHP

It probably makes me a bad programmer, but I still don't get unit tests. I get what they do, of course, but I haven't integrated it into my development. I mean, for something that crunches numbers (and probably doesn't change program state!), it's really easy to write something that verifies the answer. Either write a different algorithm and make sure the result is the same, or check the inverse of the function (assuming that makes sense) against the input (for instance, you can test that square(sqrt(x)) == x).

But for stuff that makes network connections, messes with the database, deletes files, etc. it seems less straightforward. How do you write unit testing for a parser, which is what I've been working on for the past day or two?

Anyway, John Lim came across Simple_Test for PHP. It has a lot of examples, and since I tend to use PHP a lot, maybe it'll help me get into unit testing.

Permalink | 4 Comments | Tags: Programming | id 3863

12:28 (utc-4)

Comments

Don't feel bad. I don't get it either. I understand how to write a test for a parser. Write a test document. Deduce the expected results. Run the parser against the test document. Compare the results. I guess this could come in handy if you make lots of changes to your parser code, and want to make certain that it is parsing correctly. But, for guys like you and me, just running it once will tell me whether it's parsing correctly: I don't need a unit test to tell me that.

Maybe I've missed the point, some how.

∴ Reverend Jim | 9-May-2003 12:49pm est | http://revjim.net/ | #2032

You have to try it!

You say you ran a comparison test. Did you use diff on the results or inspect it by eye? If you typed diff at the keyboard then you can make it a script. If you make it a script, you can run it again, perhaps after trying out a change.

Did you break anything? No? Try another change. hey, you don't have to think so much anymore. Did you break it this time? Yes? Where is the bug? It's in the line you just changed so debugging has become easier.

When the test works, you get faster, when it fails debugging is faster. Why throw it away the test? It's just so damn useful!

(Oh yes, you don't have to write the tests at the end so you save even more time)

yours, Marcus.

p.s. Sorry to sound preachy, but really - you have to try it. Eric Gamma describes it as test infected.

∴ Marcus Baker | 9-May-2003 8:33pm est | http://www.lastcraft.com | #2033

The best explanation of unit testing I've ever seen is the one in Dive Into Python:

http://diveintopython.org/roman_divein.html

It has a superb example and describes the unit testing process in depth. That said, I am yet to use the technique myself (although I really need to try it out some time this weekend for a university project).

∴ Simon Willison | 10-May-2003 5:24am est | http://simon.incutio.com/ | #2035

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