Behavior-Driven Development (BDD) Framework for Terraform

Behave is a Python-based behavior-driven development (BDD) framework for writing human-readable tests that describe the expected behavior of software systems. On the other hand, Terraform is an infrastructure as code (IaC) tool that streamlines the management of infrastructure by enabling developers to define resources and configurations in a declarative manner. By combining Behave's BDD approach with Terraform, you can ensure that infrastructure behaves as expected under various conditions. This integration facilitates early detection of issues and the reliability of infrastructure code.

Using Behave for Terraform Testing

Testing Terraform configurations with Behave involves a series of structured steps:

Install Behave

Begin by installing Behave and its dependencies using pip, Python's package manager. This step ensures that Behave is ready for use in the testing environment.

      pip install behave

Set up Directory Structure

Organize the test files and Terraform configurations in a directory structure that Behave expects. This structure typically includes separate directories for features, steps, and Terraform files, ensuring clarity and organization. For example:

.

├── features

│   └── terraform.feature

├── steps

│   └── step_implementation.py

├── terraform

	└── main.tf
    

Write Feature Files

Utilize Gherkin syntax to write feature files that describe the desired behavior of Terraform configurations. These feature files outline scenarios and steps that test various aspects of the infrastructure code. Here's an example terraform.feature file: 

  Feature: Verify EC2 actions
  
  	Scenario Outline: Check if the EC2 actions are allowed

    	Given I invoke <service>:<action>

    	When the region selected is <region>

    	Then the status should be <result>

Implement Step Definitions

Develop step definitions in Python to define the behavior of each step outlined in the feature files. These step definitions interact with Terraform commands, allowing for the execution of infrastructure operations and verification of results. Here's an example step_implementation.py file:

import os

from behave import *

 

@given('I invoke {service}:{action}')

def step_impl(context, service, action):

    context.action_name = ''.join([service, ':', action])

 

@when('the region selected is {region}')

def step_impl(context, region):

    os.environ['AWS_DEFAULT_REGION'] = region

 

@then('the status should be {result}')

def step_impl(context, result):

 action_name = []   

        action_name.append(context.action_name)

 		#Add assertions or checks for the action and results

Run Tests

Navigate to the root directory of the tests and execute Behave to run the defined scenarios against the Terraform configurations. During this step, Behave initializes and starts processing your test files. It reads the feature files written in Gherkin syntax to understand the scenarios you've defined. Behave executes each scenario defined in your feature files. It matches each step in the scenario to the corresponding step definition in your Python code and executes them sequentially.

behave

Review Test Results

Upon test execution, For each scenario defined in the feature files, Behave reports whether the scenario passed or failed. It also provides details about any steps within the scenario that failed, including the step definition and the error message. Review these results to ensure that the Terraform configurations behave as expected and meet the desired criteria.

Conclusion

By following the structured approach outlined above, you can leverage Behave for functional testing of Terraform configurations. This process facilitates the identification of potential issues or deviations from expected behavior, ultimately enhancing the correctness and reliability of infrastructure code. With Behave and Terraform working together, developers can adopt a systematic approach to testing and ensure the robustness of their infrastructure deployments.