Fitnesse and Slim

Fitnesse is a rather nice testing tool. It's been around since what seems like the beginning of the integration testing movement. It's based around HTML tables that are translated into application code. The wiring that translates tables into code are called fixtures. Since Fitnesse was written in Java, it was mostly useful for testing Java code, although many translations and tricks were devised to allow tests of other languages. Fitnesse also includes a wiki to make the process of creating the test tables easier.

A few years after Fitnesse was introduced, an alternate translation tool, SLIM, was created. The idea behind Slim was to allow testers to implement tests in their language of choice, with the communication between Fitnesse and the tests taking place over a socket. This allows any application that implements the correct protocol to run tests written in Fitnesse tables.

Several applications were created to support the protocol in various languages, including RubySlim for Ruby and WaferSlim for Python. I had occasion to write a set of integration tests recently, so I thought it would be simple to set up a Slim server to get the tests running. Turned out, I was wrong.

For my tests, I wanted to set up the simplest thing that could possibly work. So what is the minimum requirement for a Slim test page? If you look at the RubySlim documentation you end up with a page that looks something like this:

    !define TEST_SYSTEM {slim}
    !define TEST_RUNNER {rubyslim}
    !define COMMAND_PATTERN {rubyslim}
    !path your/ruby/fixtures 

    !|import|
    |<ruby module of fixtures>|

    |SomeDecisionTable|
    |input|get output?|
    |1    |2          |

What all these things do is not clearly explained. Click the test button; you get a bunch of cryptic error messages. So what do they mean?

Well, the first line is pretty clear: if you want to use Slim, you need to set the test system. For the rest of it, we pretty much need to go directly to the source code. It turns out that the heart of Slim is in the Java class ProcessBuilder. In the CommandRunner class of Fitnesse we find:

ProcessBuilder processBuilder = new ProcessBuilder(command);

The command argument is no more than the COMMAND_PATTERN variable defined on the page, with a single argument appended, a port number. So if you wanted to use WaferSlim (a Python Slim server), you might say:

!define COMMAND PATTERN {python /home/benfulton/slim-init.py}

(Since we need to understand how Slim works, let's get the WaferSlim source from Github rather than installing it via Pip. The slim-init source is from this gist.)

So, after downloading WaferSlim and the code from the gist, we should be able to get the Simplest Possible Page to work. Here it is:

!define TEST_SYSTEM {slim}

!define COMMAND_PATTERN {python /home/benfulton/slim-init.py }

!|import |

|RubySlim|

|app|

Click the test button, and you should get a green test.

If you don't, you may have a Slim versioning error. Go to protocol.py and change the version number from 0.1 to 0.3. Or Python may not be in your path, or the init-script may not be found. Or - here's a tricky one - you put a space before the python command. If you did that, the first command that gets passed to the ProcessBuilder class will be an empty string, and it won't run. Still, this will run green without too much effort.

But wait! What's the use of this import statement that went green before we wrote anything?