RailsConf08: Testing and Contributing to Open-Source

Yesterday afternoon I attended a lecture and workshop on how to contribute to open-source projects and associated testing tools. I want to briefly share with you some of the tools and philosophies.


rcov. rcov example rcov is a code coverage tool for Ruby. The idea is that you run it on your tests. Lines that get executed are green and “ok” and lines that are never executed are marked red for being dangerous because they are never tested. This is an easy way for you to clearly see which lines of code are never being touched by any of your test cases.

I think that rcov will significantly change the way I approach testing with my own team and consultants. I’ll have to talk to my team, but it seems reasonable to me that every piece of code that is going to be used in production should have at least 50% code coverage. In growing, changing production systems this seems like a very valuable way to keep the code malleable (because you can refactor with less fear of breaking) which then leads to increased confidence and reduced cost-of-ownership.


flog – a ruby code complexity analyzer. Now the first question you may be asking is “what in the world is a complexity analyzer?” The idea is that flog reads your code and assigns it a score based on criteria which is determined by its author, Ryan Davis. Basically it rates on the type of code Ryan Davis likes to see. This isn’t as terrible as it may sound because Ryan has some very tasteful ideas on what readable code looks like.

You may or may not agree with the way Ryan scores things, but as our speaker pointed out, flog and rcov often agree with each other about where a program’s problem areas are. More often than not the high flog score areas are not tested because they are too bulky to be tested. When one writes tests you often have to design the code in smaller, more testable pieces. Readability and testability often go hand in hand.

When running flog it can be helpful to just grep the output for #. This will give a high level view of the methods and their scores. Good candidates for refactoring are methods with scores between 80-150. Higher than 150 are typically serious problem areas (in terms of readability). Make sure you have them very well tested before you try to refactor them too much.


From the heckle website: “Heckle is a mutation tester. It modifies your code and runs your tests to make sure they fail. The idea is that if code can be changed and your tests don’t notice, either that code isn’t being covered or it doesn’t anything.” The idea is that hackle tests your tests and makes sure you are actually writing tests that are meaningful.


tarantula is a “fuzzy spider”. It crawls your web application and submits tons of garbage data and tries raise exceptions in your rails application. The premise of this tool is that no matter what data is posted, your application should not be returning 500 errors. You should handle bad data gracefully and not let unnecessary exceptions bubble to the surface. (I’m not entirely clear on how this gels with RESTful development where one often uses the return status codes to return meaningful information)


It was pointed out that none of these tools replace thought; they are here to enhance it. flog, for instance, is a tool that helps enhance your sense of code-smell. You may run flog, look at a “complex” method and decide that it is perfectly acceptable for your system. Obviously, you as the programmer know better than an automated tool. However, it is often the case that flog will point out passages of code that are challenging and difficult for anyone but the original author to read. The idea is to encourage code that is simple to test, read, and understand. This makes the code more robust and open to change.

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  • Matt Pulver

    Very cool! These tools are all new to me; I appreciate you sharing them.