Learning and Development: Terraform Testing

This repository contains necessary documentation to perform automated tests on Terraform scripts.

• Author: Sakthi Santhosh
• Created on: 26/12/2023

Introduction

terraform test has been introduced with Terraform V1.6 and it is used to test Terraform scripts. Unlike terraform plan and terraform apply, testing is done locally on an ephemeral infractructure on memory. Various assertions can be placed in testing scripts to ensure desired behaviour.

Terraform Setup

In this repository, Terraform scripts have been written to provision a static website in a S3 bucket.

Testing Scripts

• Terraform looks for testing scripts in the ./ (root) or ./tests/ directory. Inside these directories, it looks for *.tftest.hcl file and executes them.
• Setup work for tests can be written as same as the provisioning scripts. These are called helper modules. For this project, the setup scripts for testing can be found at ./tests/setup/ directory. Here, we're creating a random prefix for S3 bucket as a setup process.
• In the test file, there are run blocks which represent a step in the process of provisioning. Inside this block, we can have multiple assert blocks that validate the correctness of the step.
• The run.create_button block assets three conditions:
  1. Bucket Name
  2. eTag of index.html (hash matching with local and bucket file)
  3. eTag of error.html (hash matching with local and bucket file)
• This block uses the apply command because we cannot test the assertions without applying (provisioning) the infrastructure.
• Values to variables can be assigned inside the run block. For example, the variable named bucket_name defined in ./variables.tf is assigned a value here. The default value is overidden by this.
• The run.website_is_running block requires the ./tests/final/ helper module. This helper module makes a request (with data block in ./tests/fina/data.tf) to the website URL created by the previous run block. This URL is accesses from the run block which references it from the output block in ./outputs.tf.
• Here, the command applied is plan as the website is already running (from previous run block) and plan command lists out the execution plans alone which is sufficient for the assertions made in this block.

Contributing

This is a personal project and I discourage public contributions. The repository has been kept public only for learning purpose.