Using Cucumber and Perl to define test cases in natural language

Scenarios Still Without Actions

Once Cucumber is installed (see the "Installation" section), impatient developers can launch the test suite on a trial flight. To do so, you need to call the cucumber program in the directory above the features directory, in which the basic.feature file shown in Listing 1 resides.

Of course, Cucumber has at this time no idea what actions it needs to perform based on the feature description, because the step definitions are still missing. However, it tries to help out by sketching in some Ruby code, as shown in Figure 1.

Figure 1: The Cucumber tool gives programmers a helping hand if Cucumber step definitions are missing.

Each text entry after Given, When, or Then describes a scenario. Interestingly, Cucumber treats these keywords in the same way and only uses the assigned step definition. The different designations are only used to formulate the requirements understandably for the user.

Perl Without Gloss

The Perl implementation, with the aid of the CPAN Test::BDD::Cucumber [4] module, lacks a bit of the elegance of its role model but gets the job done. To start the test suite, the Perl programmer does not call cucumber as in the original Ruby version; instead, it calls a script named pherkin, which is included with the module and probably a synthesis of "Perl" and "gherkin." The output in Figure 2 uses gray text for nonfunctioning scenarios to make perfectly clear which step definitions are missing.

Figure 2: Without step definitions, pherkin only greys out the scenario.

Listing 2 shows the step definition, which snaps up the text after the Given expression in the background description. The file must have an extension of .pl and reside in a directory called step_definitions below features.

Listing 2 – Definition 1


The regular expression squashed between Given qr/ and / in line 6 searches for a string (a usable <[...]> class) in all scenarios of the feature. In case of a match, the class name grouped by the brackets in (\S+) lies in the $1 variable, and use_ok() checks in line 7 whether the class can be loaded on the system using use Yahoo::FinanceQuote.

The auxiliary function use_ok() comes courtesy of the standard Test::More module. In typical Perl TAP format style, it outputs ok  1 if all goes well, and not ok  1 if an error occurs. The pherkin tool understands this format and highlights the feature text in green or red accordingly.

Figure 3 shows that the background statement executed before the actual scenario is now highlighted in green, whereas the two scenarios that follow – When [...] and Then [...] – are still gray, or undefined.

Figure 3: Only the background statement runs without an error, because the submitted scenarios still lack a step definition.

Listing 3 delivers the rest of the step definitions in order to fully process the feature file in Listing 1. The pherkin script imports Given, Then, And, and other commands before calling the step definitions; the user does not need to include extra modules for this. Note that the two steps in the Retrieve Facebook scenario depend on each other because the first step retrieves the share price from the server, and the second compares the numeric value with a preset in the scenario text.

Listing 3 – Definition 2


An Exchange with Context

The two steps communicate with one another via a context that pherkin provides in the $c variable if – as in line 5 of the steps definition in Listing 3 – the Method::Signatures module is loaded and the function to be called is declared using func($c) {} (instead of sub{} as shown in Listing 2). The method stash() retrieves a reference to a memory area, which provides space for data generated in one step and needed in another under the scenario key.

In Listing 3, the When step stores the share price retrieved from the Yahoo server by the getonequote() function of the Finance::YahooQuote module below the context's quote key. The Then step picks it up again from this location in line 24. The ok() function from Test::More checks in line 15 whether a share price has arrived, and in line 24 whether it is greater than the value set in the text.

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