Eric Lefevre-Ardant on Java & Agile

After an initial introduction video, one on comparaison operators, Bob Martin has now a video on Data Types in Slim, his Fit replacement in Fitnesse.

Data types in Slim are simple. They can only be Strings and Lists, though it is entirely possible for fixtures to actually get integers.

A list looks like this:

[1, 2, 0.5]

Note the brackets. Also, note the space between the comas and the following value. This is important, as the comparaison will actually be made between the exact string specified in the table, and the String representation of the List returned by the fixture. Hence, the format in toString() is important.

Now that the release of Slim is done, Bob Martin is spending time producing tutorial videos. The new one is about comparaisons in Slim.

There are two majors things to learn in it:

• approximate equals
• ranges

The ~= sign means “approximately equals to”, and depends on the number of decimals; for example,

~=1.3

in a cell will work for any value between 1.2 and 1.4.

A range allows Slim to accept results between boundaries. For example, put something like

1<_<8

in a cell and all values between 1 and 8 will be considered valid. This is something that some versions of Fit could do, but not all. With Slim, all versions of Slim will support this (since it will be evaluated on the Fitnesse side).

Last thing: Fitnesse contains a rather powerful expression evaluator that is not specific to Slim or Fit.
For example:

!define TIMES {1000}
|${=5*${TIMES}=}|

You can combine this construct with the range, and have something like this in your cell:

${=5*${TIMES}=}<_<${=6*${TIMES}=}

which will appear as

5000<_<6000

when viewing your wiki page.

Finally, you might want to watch out for the coming minor release of Fitnesse.

You are probably familiar with Fitnesse, a wiki site that wraps Fit. It is basically an environment that helps attaching tests to specifications. Some call this a Test-Driven Requirements (TDR) tool. It has been originally written by Robert C Martin (aka Uncle Bob), Micah Martin and Michael Feathers.

Well, Uncle Bob is coming back with Slim, an extension of Fitnesse he has been working on since August 2008, as his followers on Twitter know. It has been released in the latest version of Fitnesse a few days ago.

Simply put, Slim (Simple List Invocation Method) is an alternative to Fit, quite simpler to implement and to use, and integrated with Fitnesse.

The big thing with Slim, for us mere users, is that it calls POJOs. No need to inherit from Fit-specific classes anymore! (something that GreenPepper has had for a long time) You will just have to implement some methods with particular names, depending on the type of fixture you use.

The fixtures that are available are familiar ones:

• Decision Table, the equivalent of Column Fixture, with input columns and output columns
• Query Table, the equivalent of Row Fixture; interestingly, its method query() now returns a List of Lists of Lists (!) instead of an Object[]  table
• Script Table, the equivalent of Do Fixture in FitLibrary; it also shares many caracteristics with ActionFixture
• finally, Table Table is the way for you to write any arbitrary fixture

Other enhancements include:

• variables in fixtures can stay private; no need for them to be public anymore; setter methods are required instead. Not a big deal in my view, but something that beginners were often complaining about
• error messages are clearer in Fitnesse, typically when classes or methods cannot be found in the fixtures
• as a side effect of an evolution of Fitnesse made necessary by Slim, it is now possible to run tests in differents JVMs
• Slim is much simpler to implement than Fit is; this is supposed to make ports of it to other languages much easier, more stable, and more consistent (some implementations of Fit do not have the exact same features as others)
• it should also be possible to write tests without tables (with updates of Slim), which was very difficult with Fit, because of all these implementations; I want to see things like the plain text tests in TextTest !

Convinced? Then the next step for you is to look at the tutorial video Bob Martin did yesterday.

Me, I think this is a great enhancement, and one of the biggest news in the TDR Tools world this year. With Bob Martin’s influence, there is no doubt it will pick up steam quickly.