Something To Do Before You Unit Test

Monday, June 9. 2008

At DCPHP, I saw several clever presentations about unit testing, which essentially reinforced what I already know: if I could go back in time and actually guide the development of the CMS we had built in-house, I'd structure it not to have clever self-references and three-level inheritance...which would, incidentally, make it something less than a three-year project to create unit tests for it.

But over the years, with many beginning developers coming through our doors, I've seen several things that the guys who advocate unit testing assume you, as a sane person, are doing...but mostly I've seen those things not being done. So here's an easy one:

<?php
$sql = "SELECT id, name, type FROM people LIMIT 10 ORDER BY date_added DESC";
$result = mysql_query($sql);
 
if (mysql_num_rows($result))
{
    // do stuff
}
?>

Great, eh? Checking to see if there are actually rows returned before you do something, right?

But what if your query fails? Remember, you write code not just for right now, but for when you do things down the line. Just like you make unit tests to catch any screwups before you go to production, you can be testing any calls right inside your code. So later, when you add "just a quick fix" and screw up the query, it doesn't have to fail if, for example, it only fails when you pass a variable in and the tests you wrote originally don't cover that.

So always be paranoid about any queries you make:

<?php
$sql = "SELECT id, name, type FROM people LIMIT 10 ORDER BY date_added DESC";
$result = mysql_query($sql);
 
if (false === $result)
{
    // handle gracefully
}
elseif (0 < mysql_num_rows($result))
{
    // do something
}
else
{
    // handle the case of no data
}
?>

Obviously, in the world of PHP 5 and OO, you should be using exceptions and try-catch, but it is amazing to me the number of developers who will blithely assume their queries are perfect and will remain so, and that there's no risk they'll ever see a production box. Testing is one of the first thing a schedule- or budget-pressed project will skimp on when resources go short. Most clients react less well to "we had to cut your feature, because the budget is running low" than "no problem with your feature, we'll just do some spot checks instead of the full-on testing process." That is, they will until you screw up and they discover a page is completely unusuable on a weekend when you're off paddling down a river.

So write fault-tolerant code. Make sure that even if your query fails, you handle it in a graceful way--and that you provide yourself enough information to quickly figure out what's going on on Monday and fix the thing.

Posted by Sandy Smith in Programming at 00:57 | Comments (3) | Trackbacks (0)

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I agree with, what I think is, the gist of your argument. That is, if you don't write code that anticipates failure, you're not going to write good unit tests either.

Unit tests help in making you think about the design of your code and its components, promotes coupling items loosely, and requires adding new tests when new bugs are found or features added.

#1 Oscar Merida on 2008-06-09 11:43 (Reply)

My point isn't to bash unit tests, but rather to say there are a bunch of things you should be doing before you get around to writing your unit tests. It's a maturity model for PHP: at some point you're writing test-first, fully documented code with peer review, version control, and a rabbi's blessing. But before you get there, you should be doing basic things like sanity checking all your input and testing for errors. And if you skip those basic things, you're not going to have the right frame of mind to write the kinds of tests that will save you down the line.

#1.1 Sandy (Homepage) on 2008-06-09 11:52 (Reply)

I didn't mean to imply that you were bashing unit tests.

#2 Oscar Merida on 2008-06-09 11:56 (Reply)

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I didn't mean to imply that you were bashing unit tests.

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