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Introduction
Infrastructure as code brings the benefits of software development practices to infrastructure management. One of the most important — and most frequently neglected — of these practices is testing. Infrastructure code changes can have serious consequences, from application downtime to security vulnerabilities to unexpected cost increases. Testing your IaC before applying it to production is not optional; it is a professional responsibility. This article covers the testing strategies and tools available for modern IaC practitioners.
Why IaC Testing Is Often Skipped
Testing infrastructure code is less intuitive than testing application code. There is no obvious equivalent of a unit test for a Terraform module. Running tests against real cloud resources costs money and takes time. Many teams adopt IaC and then stop short of implementing testing, relying on manual review as their quality gate. This approach works until it does not — a misconfiguration reaches production and causes an incident that would have been caught by automated testing.
Static Analysis and Linting
The first layer of IaC testing is static analysis, which inspects your code without executing it. Terraform Validate checks that your configuration is syntactically valid. TFLint identifies potential errors and enforces best practices. Checkov scans Terraform and other IaC formats for security misconfigurations, checking against hundreds of security benchmarks. These tools run quickly and catch a wide range of common errors before any infrastructure is created.
Policy as Code with Open Policy Agent
Policy as code tools like Open Policy Agent, or OPA, allow you to define organizational policies as code and enforce them against your IaC. You can write policies that require all resources to have specific tags, prevent the creation of publicly accessible storage buckets, or enforce naming conventions. These policies run as part of your CI/CD pipeline, preventing non-compliant infrastructure from ever being deployed.
Integration Testing with Terratest
Terratest is a Go library for writing automated tests for Terraform, Packer, and other IaC tools. With Terratest, you can write tests that actually deploy infrastructure to a real cloud environment, validate that the infrastructure behaves as expected, and then tear it down. These integration tests provide high confidence that your infrastructure code works correctly but require a test environment and can take minutes to run. They are best run in CI/CD pipelines on feature branches.
Using Terraform Plan for Review
Even without sophisticated testing tools, the terraform plan command provides valuable validation. By running terraform plan in your CI/CD pipeline and surfacing the output in code review tools, you enable human reviewers to catch logical errors and unintended changes. Tools like Atlantis automate the process of running terraform plan on pull requests and posting the output as a comment, making infrastructure review as natural as code review.
Conclusion
Testing infrastructure as code is an investment that pays for itself the first time it prevents a production incident. Building a layered testing strategy — static analysis, policy enforcement, and integration testing — provides defense in depth for your infrastructure changes. Our infrastructure automation and testing experts help organizations build robust IaC testing practices. Explore our IaC best practices and testing blog for more.
