Freek Lijten has a new post today continuing his look at the world of PHP extensions and focusing in on testing this time. He hopes to answer the question of what makes a good, effective set of tests to help increase the stability and quality of the extensions you write.

In my previous blog I took you through the process of getting PHP and extensions compiled, generating code coverage and running tests. What I did not talk about was what makes a good test. I hope to correct on this by adding this post and going into more detail on the actual writing of tests itself.

Using the same extension as before (enchant) he goes through the addition of a test for the enchant_dict_add_to_session function. He start by showing how much the function is currently tested (hint: none) and code coverage. He points out that 100% coverage is just one metric in a set that should be considered and not the final goal. He shares a simple test for the function that checks to see if a certain word exists in a dictionary. The coverage report shows all lines being executed, but there's a lot not tested, at least conceptually. He shows how to test "the spirit" of the function with additional tests for non-existent words, spell checking and if a word is not in the dictionary at all. PHP example code shows these tests kinds of tests to illustrate the steps he's talking about.