Tutorial 3: Step Parameters

Goal:Use step parameter to handover parameters to step functions.

Write the Feature Test

# file:features/tutorial03_step_parameters.feature
Feature: Step Parameters (tutorial03)

  Scenario: Blenders
    Given I put "apples" in a blender
    When  I switch the blender on
    Then  it should transform into "apple juice"

The feature description contains a number of parameters, where different values can be filled in. This also makes the test automation layer much simpler, because the number of step definitions is reduced.

Hint

BEST PRACTICE: Put parameters in double-quoted text to make variation-points visible. The test runner output does not have this problem, because it often marks these parameters as bold text.

Provide the Test Automation

# file:features/steps/step_tutorial03.py
# ----------------------------------------------------------------------------
# STEPS:
# ----------------------------------------------------------------------------
from behave   import given, when, then
from hamcrest import assert_that, equal_to
from blender  import Blender

@given('I put "{thing}" in a blender')
def step_given_put_thing_into_blender(context, thing):
    context.blender = Blender()
    context.blender.add(thing)

@when('I switch the blender on')
def step_when_switch_blender_on(context):
    context.blender.switch_on()

@then('it should transform into "{other_thing}"')
def step_then_should_transform_into(context, other_thing):
    assert_that(context.blender.result, equal_to(other_thing))

Provide the Domain Model

# file:features/steps/blender.py
# -----------------------------------------------------------------------------
# DOMAIN-MODEL:
# -----------------------------------------------------------------------------
class Blender(object):
    TRANSFORMATION_MAP = {
        "Red Tree Frog": "mush",
        "apples": "apple juice",
        "iPhone": "toxic waste",
        "Galaxy Nexus": "toxic waste",
    }
    def __init__(self):
        self.thing  = None
        self.result = None

    @classmethod
    def select_result_for(cls, thing):
        return cls.TRANSFORMATION_MAP.get(thing, "DIRT")

    def add(self, thing):
        self.thing = thing

    def switch_on(self):
        self.result = self.select_result_for(self.thing)

Run the Feature Test

When you run the feature file from above:

$ behave ../features/tutorial03_step_parameters.feature
Feature: Step Parameters (tutorial03)   # ../features/tutorial03_step_parameters.feature:1

  Scenario: Blenders                            # ../features/tutorial03_step_parameters.feature:3
    Given I put "apples" in a blender           # ../features/steps/step_tutorial03.py:39
    When I switch the blender on                # ../features/steps/step_tutorial03.py:44
    Then it should transform into "apple juice" # ../features/steps/step_tutorial03.py:48

1 feature passed, 0 failed, 0 skipped
1 scenario passed, 0 failed, 0 skipped
3 steps passed, 0 failed, 0 skipped, 0 undefined
Took 0m0.000s