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A pure-erlang, open-source, 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...

./rebar3 compile

To run unit tests, do...

./rebar3 eunit

There's are sample feature files (examples/complex_sample/features and examples/complex_sample/features) and step definitions (in examples/src). Running make test will execute these too.

You can also run them by hand, for example...

examples $ ../cucumberl
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
    And I have entered 70 into the calculator                    :8
    When I press add                                             :9
    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...

Action(TokenList, State, Info)

Where Action is:

  • given
  • 'when'
  • then

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

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

So for example, the previous TokenList would also be accepted in a function definition like this:

given([i, have, entered, Name, into, the, authors, field], State, _) ->
    {ok, NewState}.

The State parameter is the state the last step function returned in the state field of the tuple. In the above example, this is NewState.

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 definition functions, using erlang's pattern matching.

given([i, have, entered, N, into, the, calculator], _State, _Info) ->
  % Your step implementation here.

'when'([, i, press, add], _, _) ->
  % Your step implementation here.

then([the, result, should, be, Result, on, the, screen], _, _) ->
  % Your step implementation here.

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

  • The atoms true and ok in the state tuple represent success and print ok on the console
  • A two-tuple of the form {failed, Reason} indicates failure

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

Running cucumberl on the command line is very simple. Just execute the cucumberl self-contained escript.

To run a feature file through cucumberl using the erlang API...


For example...



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

The FeatureDefinitionModule parameter is an optional module that implements the feature and contains the step callbacks. However, it is only needed when the name of the step implementation is different then the name of the feature. For example...


is exactly equivalent to


However, you may want to implement the feature in a different module, such as ...

cucumberl:run("./features/auction.feature", some_other_module).

perfectly acceptable but not recommended.

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 files examples/simple_sample/src/simple_sample_table.erl and examples/simple_sample/features/simple_sample_table.feature for more details.


MIT - We made this for you!

Feedback, or getting in touch

Improvements and patches welcomed --

Cheers, Steve Yen


pure erlang implementation of Cucumber parser & driver




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