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pure erlang implementation of Cucumber parser & driver
Erlang Ruby
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A pure-erlang, open-source, single-file implementation of Cucumber ( This provides a subset of the Cucumber feature definition language.

Quick Start

You'll need erlang, of course.

To do a build, do...


To run unit tests, do...

make test

There's a sample feature file (features/sample.feature) and step definition (in src/sample.erl). You can try them out like this:

make sample

For example, here's a sample run...

$ make sample
erl -pa ebin -noshell -s sample main -s init stop
Feature: Addition                                                :1
  In order to avoid silly mistakes                               :2
  As a math idiot                                                :3
  I want to be told the sum of two numbers                       :4
  Scenario: Add two numbers                                      :6
    Given I have entered 50 into the calculator                  :7    ok
    And I have entered 70 into the calculator                    :8    ok
    When I press add                                             :9    ok
    Then the result should be 120 on the screen                  :10   ok

Slow Start

So you want to write your own step definitions? No problem. Any erlang module that implements step definitions should export a step/2 function, with this kind of call signature...

step(TokenList, Info)

The TokenList parameter is a list of either atoms or strings, such as...

[given, i, have, entered, "Joe Armstrong", into, the, authors, field]

The Info parameter is a tuple of helpful debug information, such as the {LineText, LineNum}, of what cucumberl is currently processing. The Info parameter is usually ignored unless you're deep into debugging your scenario/steps.

Here's how you'd write a few step defintion functions, using erlang's pattern matching.

step([given, i, have, entered, N, into, the, calculator], _Info) ->
  % Your step implementation here.
step(['when', i, press, add], _) ->
  % Your step implementation here.
step(['then', the, result, should, be, Result, on, the, screen], _) ->
  % Your step implementation here.
step(_, _) -> undefined.

Notice that all the tokens have been atomized (and turned lowercase).

Also, we must have a last step definition that returns undefined, so that cucumberl can keep matching against every module that you provide in your StepDefinitionModules list (see below).

In general, your "real" step definitions return anything but undefined.

The above step definitions will match a scenario like the following...

Scenario: Add two numbers
  Given I have entered 50 into the calculator
  And I have entered 70 into the calculator
  When I press add
  Then the result should be 120 on the screen

Running cucumberl

To run a feature file through cucumberl, the erlang API is...

cucumberl:run(PathToFeatureFile, StepDefinitionModules).

For example...

cucumberl:run("./features/sample.feature", StepDefinitionModules).

The StepDefinitionModules parameter is a list of modules that define step/2 callbacks. For example...


Scenario Outlines

There's basic support for Scenario Outlines, aka Example Tables, in cucumberl. However, placeholders names should be all lowercase, and there shouldn't be any blank lines before the "Examples:" label. For example...

Scenario Outline:
  Given I have cleared the calculator
  And I have entered <a> into the calculator
  And I have entered <b> into the calculator
  When I press <op>
  Then the result should be <ab> on the screen
    |  a | b | ab | op       |
    |  1 | 1 | 2  | add      |
    |  1 | 3 | 3  | multiply |
    |  2 | 3 | 6  | multiply |
    | 10 | 1 | 11 | add      |

See the src/sample_table.erl and features/sample_table.feature for more details.

It fits in one file!

To use cucumberl in your own work, you can just copy src/cucumber.erl to your own erlang project, as it's fully self-contained.


MIT - We made this for you!

Feedback, or getting in touch

Improvements and patches welcomed --

Cheers, Steve Yen

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