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copied!<p>I was the project lead on the Zend Framework a few years ago, through the release of ZF 1.0. I worked pretty hard on raising the coverage of testing for all components, and we had a policy that a component must have a certain minimum code coverage to be adopted into ZF from the incubator.</p> <p>However, you're right, trying to get 100% code coverage from tests for all your classes isn't really practical. Some of the classes in ZF have 100% coverage, but for these, one or more of the following was true:</p> <ul> <li>The class was trivially simple.</li> <li>The tests took extraordinary work to write. E.g. complex setup code to create conditions to exercise all the obscure corner cases. Look at the unit tests for Zend_Db that I wrote! Though it's beneficial to force yourself to test these corner cases, because I guarantee that it'll lead you to code that you need to fix.</li> <li>The class had to be refactored to be more "testable". This is often a good thing anyway, because you end up with better OO code, with less coupling, fewer static elements, etc. See the classes and tests for Zend_Log.</li> </ul> <p>But we also realized that 100% code coverage is sometimes an artificial goal. A test suite that achieves less tan 100% coverage may nevertheless be adequate. And a test suite that does get to 100% coverage doesn't necessarily assure quality.</p> <p>It would be very easy to get 100% code coverage for the following function. But did we test for division by zero?</p> <pre><code>function div($numerator, $denominator) { return $numerator / $denominator; } </code></pre> <p>So you should use code coverage as one <em>metric</em> of testing, but not the ultimate goal.</p>

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