behave-classy

Installation

Installation is made easy with pip

pip install behave-classy

What is behave-classy

beahve-classy provides a class-based API for behave step implementations

This package is geared towards authors of step implementation libraries and aims to provide a more flexible and extensible interface for behave step libraries and their users.

The primary features

• ability to define step definitions as classes
• ability to extend steps from your own classes (or perhaps classes provided by other libraries/packages)
• ability to define a matcher per-method without changing global state of the 'current matcher'
• wraps methods to transform context into an attribute (self.context), so it's not necessary to have each method use context as first parameter in the signature. Works with default behave runner.

Usage

Usage is fairly simple and follows these basic steps:

• Use the step_impl_base to create a base class that will contain your step definitions in its own local registry.
• Make your subclass and definitions
• When you want to use your steps, simply call the register method of your class.

Example

Consider some step library which provides a set of steps in the class BankAccountSteps.

#  some_library/steps.py
from behave_classy import step_impl_base

Base = step_impl_base()

class BankAccountSteps(Base):
    @Base.given(u'I have a balance of {amount:d}')
    def set_balance(self, amount):
        self.balance = amount
    
    @Base.when(u'I deposit {amount:d} into the account')
    def deposit(self, amount):
        if amount < 0:
            raise ValueError('Deposit amounts cannot be negative')
        self.balance += amount
    
    @Base.when(u'I withdraw {amount:d} from the account')
    def withdraw(self, amount):
        self.balance -= amount
    
    @Base.then(u'the balance should be {expected_amount:d}')
    def check_balance(self, expected_amount):
        assert self.balance == expected_amount

    @property
    def balance(self):
        """convenience shortcut for context balance"""
        amount = getattr(self.context, 'balance', 0)
        return amount
    
    @balance.setter
    def balance(self, new_amount):
        """convenience setter"""
        self.context.balance = new_amount

As a user of such a library, you would import the class, then register it, so its definitions are added to the global step registry used by behave.

# myproject/features/steps/mysteps.py
from some_library.steps import BankAccountSteps
BankAccountSteps().register()

Then with a typical feature file...

# myproject/features/account_balance.feature
Feature: bank account balance
  Background: 
    Given I have a balance of 100
    
  Scenario: withdraw
    When I withdraw 42 from the account
    Then the balance should be 58
  
  Scenario: deposit
    When I deposit 42 into the account
    Then the balance should be 142

You can simply run behave as normal

$ behave

Feature: bank account balance # features/account_balance.feature:2

  Background:   # features/account_balance.feature:3

  Scenario: withdraw                    # features/account_balance.feature:6
    Given I have a balance of 100       # features/steps/steps.py:18
    When I withdraw 42 from the account # features/steps/steps.py:28
    Then the balance should be 58       # features/steps/steps.py:32

  Scenario: deposit                    # features/account_balance.feature:10
    Given I have a balance of 100      # features/steps/steps.py:18
    When I deposit 42 into the account # features/steps/steps.py:22
    Then the balance should be 142     # features/steps/steps.py:32

1 feature passed, 0 failed, 0 skipped
2 scenarios passed, 0 failed, 0 skipped
6 steps passed, 0 failed, 0 skipped, 0 undefined
Took 0m0.002s

extending and integrating existing work

Without behave-classy, you would typically use behave's context.execute_steps feature to extend on work. Although this works for simple cases, it can be quite inflexible, especially once your cases become nontrivial. behave-classy allows you to use usual python techniques (e.g. subclassing, method extensions/overriding, etc.) to reuse your existing code, just like you would do in any other python code.

Consider the Bank Account example from the previous section. This example demonstrates several features:

1. We will add additional steps the class, adding new methods, which reuse existing methods. One of these will use a different matcher, the RegexMatcher.
2. We will extend the existing withdraw method to first check that the account has sufficient funds, otherwise raising a ValueError.
3. We will integrate unittest assertion matchers to the class by using unittest.TestCase as a mixin
4. We will override the existing check_balance method to use unittest.TestCase assertions

# myproject/features/steps/mysteps.py
from unittest import TestCase
from behave.matchers import RegexMatcher
from some_library.steps import BankAccountSteps as Base

class ExtendedSteps(Base, TestCase):
    def withdraw(self, amount):
        """Extends withdraw method to make sure enough funds are in the account, then calls withdraw from superclass"""
        if amount > self.balance:
            raise ValueError('Insufficient Funds')
        super().withdraw(amount)
    
    def check_balance(self, expected_amount):
        """Override check_balance method to use unittest assertions instead"""
        self.assertEquals(self.balance, expected_amount)
        

    @Base.when(u'I pay my {loan_name} loan payment')
    def pay_loan(self, loan_name):
        """additional when step for loan payments"""
        loan_payments = {
            'student': 600,
            'car': 200
        }
        payment_amount = loan_payments[loan_name]
        self.withdraw(payment_amount)


    @Base.then(u'the balance should be (less|greater) than (or equal to )*(\d+)', matcher=RegexMatcher)
    def compare_balance(self, operator, or_equals, amount):
        """Additional step using regex matcher to compare the current balance with some number"""
        amount = int(amount)
        if operator == 'less':
            if or_equals:
                self.assertLessEqual(self.balance, amount)
            else:
                self.assertLess(self.balance, amount)
        elif or_equals:
            self.assertGreaterEqual(self.balance, amount)
        else:
            self.assertGreater(self.balance, amount)


ExtendedSteps().register()

We'll add some additional scenarios to our feature file to show off these new alterations

# myproject/features/account_balance.feature
# ...
  Scenario: pay loans
    Given I have a balance of 1000
    When  I pay my student loan payment
    Then  the balance should be less than 1000
    When  I pay my car loan payment
    Then  the balance should be greater than or equal to 1

  Scenario: failing unittest assertion (expected to fail)
    # this is expected to fail, to show off the unittest assertion at work
    Given I have a balance of 100
    Then  the balance should be greater than 100


  Scenario: withdrawing more than balance raises ValueError (expected to fail)
    #  this is expected to fail with a ValueError to show off the extended withdraw method
    Given I have a balance of 100
    When  I withdraw 500 from the account

Then if we run this using behave...

$ behave
Feature: bank account balance # features/account_balance.feature:2

  Background:   # features/account_balance.feature:3

  Scenario: withdraw                    # features/account_balance.feature:6
    Given I have a balance of 100       # features/steps/steps.py:25
    When I withdraw 42 from the account # features/steps/steps.py:58
    Then the balance should be 58       # features/steps/steps.py:45

  Scenario: deposit                    # features/account_balance.feature:10
    Given I have a balance of 100      # features/steps/steps.py:25
    When I deposit 42 into the account # features/steps/steps.py:29
    Then the balance should be 142     # features/steps/steps.py:45

  Scenario: pay loans                                     # features/account_balance.feature:14
    Given I have a balance of 100                         # features/steps/steps.py:25
    Given I have a balance of 1000                        # features/steps/steps.py:25
    When I pay my student loan payment                    # features/steps/steps.py:48
    Then the balance should be less than 1000             # features/steps/steps.py:64
    When I pay my car loan payment                        # features/steps/steps.py:48
    Then the balance should be greater than or equal to 1 # features/steps/steps.py:64

  Scenario: failing unittest assertion (expected to fail)  # features/account_balance.feature:21
    Given I have a balance of 100                          # features/steps/steps.py:25
    Given I have a balance of 100                          # features/steps/steps.py:25
    Then the balance should be 10                          # features/steps/steps.py:45
      Assertion Failed: 100 != 10


  Scenario: withdrawing more than balance raises ValueError (expected to fail)  # features/account_balance.feature:27
    Given I have a balance of 100                                               # features/steps/steps.py:25
    Given I have a balance of 100                                               # features/steps/steps.py:25
    When I withdraw 500 from the account                                        # features/steps/steps.py:58
      Traceback (most recent call last):
        <partially omitted for readme brevity>
        File "features\steps\steps.py", line 61, in withdraw
          raise ValueError('Insufficient Funds')
      ValueError: Insufficient Funds



Failing scenarios:
  features/account_balance.feature:21  failing unittest assertion (expected to fail)
  features/account_balance.feature:27  withdrawing more than balance raises ValueError (expected to fail)

0 features passed, 1 failed, 0 skipped
3 scenarios passed, 2 failed, 0 skipped
16 steps passed, 2 failed, 0 skipped, 0 undefined
Took 0m0.008s

We can see our additional scenarios ran and observe the following from the results:

1. Our additional loan payment steps ran as expected
2. Our step definition compare_balance, using the RegexMatcher, correctly matched our steps in the feature file
3. Our override of the check_balance method worked and used unittest assertion (evidenced in the failure case)
4. Our extended withdraw method was successfully used as expected (demonstrated by the failing case with ValueError)