Perl Hacks

Hack #65. Test Live Code

Verify your code against actual use...with little penalty.

Perl culture widely acknowledges automated testing as one step in verifying quality. Most CPAN modules and many large applications, not to mention Perl distributions themselves, have comprehensive test suites that run before installation to show what works and, occasionally, what doesn't work.

In theory, that's enough. In practice, it can be difficult to predict exactly how your code will react to production systems, live customers, and their actual data. Testing against this scenario would be incredibly valuable, but it's much more complex—not to mention probably much slower. If your automated tests are effective, they'll match the behavior of most customer requests.

Fortunately, it's possible to embed tests in production code that test against live data, non-destructively, but that don't generate too much data nor slow down your system.

The Hack

Imagine you have a web application that allows employees to manage their user data stored in a backend LDAP database. Abstraction is the key to a good system. You've created a User object and you've tested that the system vets and verifies all sorts of names and addresses that you could think of. You don't know how the system will react to the messy real world, though.

Instead of hard-coding the creation of the User object, create a factory object that returns a User object or equivalent.

package UserFactory; use User; use UserProxy; my $count = 0; sub create ...