Software metrics (PHP focused) part 2

NOTICE: Find more in my tech blog: liopic.me.

In part 1 I spoke about lines of code and average of lines per day. Two indexes that are quite naive. Let’s see some better metrics, most of them object oriented programming focused.

Third stop: Tests and code coverage
If you have unit tests you can easily control that nothing vital is broken in each contribution. A unit test stress a class, so if there is some change in it, you can verify that the expected behavior remains the same. Moreover you can get an analysis of which lines of the code are actually executed in a test suite: that is, the code coverage of the test. You will see high values in well tested classes and low values in classes that need more tests.

Tools? Of course, PHPUnit, with the help of xdebug to get the code coverage.

Four stop: Cyclomatic complexity
Cyclomatic complexity is just the amount of different paths the execution can go throughout. For example, in our main project we have a total of 3048 paths. This value can be interesting to detect places in code that have become too complex and maybe need some cleanup.

Five stop: Pure OO software metrics
There are some interesting software metrics for object oriented code organized in packages, used basically to value which packages (groups of classes) are of better quality than others. Values that show the relation among classes, dependences, the resilience to change, etc.

Last stop: Ratios
Combining some of the previous values you can get interesting ratios. For example:
– Cyclomatic complexity per lines of code: 0.2, a very good value.
– Lines of code per method (class function): 22.02, a normal value that we have to lower.
– Method per classes: 8.25, a good value.
– Average number of extended classes: 0.4, a good value.
– etc…

Tools? The excellent pdepend is used here. Have a look at the end of its example page to see the amount of data (and funny but interesting diagrams) you can get.

Finally, all those values and tests are compiled each single time a programmer sends a commit to our code repository, and I get a mail with all the details, including the lines added, the author’s name, and all the values that change. So with a quick look I can assure that the contribution is ok, or there is some code to improve. I wonder how many companies (which develop in PHP) use something like this. I bet less than 100 in the world!