A Comprehensive Guide to Testing in Terraform Keep Your Tests, Validations, Checks, and Policies in Order

Summary

You have many options to use when it comes to testing and validating your Terraform configurations and modules. The newest addition to these options is the native Terraform testing framework. This in combination with custom conditions, check blocks, and policies allow for creating robust infrastructure-as-code. This post is a comprehensive guide to testing and validation in Terraform.

Highlights

. These constrains could be to limit the length of a supplied string to less than ten characters, or to restrict the allowed values of a variable to a predefined list of values. Resources and data sources have the lifecycle block where you can add precondition and postcondition blocks to validate things before, and after, running an apply, respectively. Similarly, you can add precondition blocks to your output blocks, to validate something about the output value. ([View Highlight] (https://read.readwise.io/read/01hg6s3461nma2q6d635xgnarh))

In the precondition block I check that the managed_by property of the resource group is set to the value terraform. If the managed_by property has any other value, the condition will evaluate to false and the precondition fails. The operation will halt and the error_message is displayed to the user in the console. ([View Highlight] (https://read.readwise.io/read/01hg6s7wjry1pcb4m7fdhsjnj5))

Tests are written using HCL, so you do not need to learn a new language in order to test your IaC. Test files use the .tftest.hcl file ending.
By default, all test files stored in the same directory as your module, or stored in a tests directory, are run when you issue the new terraform test command. If you place your tests in a different directory you can add the -test-directory=path/to/my/test/directory flag to the command. ([View Highlight] (https://read.readwise.io/read/01hhavh4nktk1yqeszf2qw35nm))

A test file consists of one or more run blocks. Each run block should be thought of as a test. A run block includes a number of arguments and blocks to configure what the test should do. Each test executes a command, which is either plan or apply. If you do not specify the command argument it defaults to apply. ([View Highlight] (https://read.readwise.io/read/01hhavhexyfpgq7jkj74k09cxe))

The concept of checks together with the check block was introduced in Terraform 1.5 and serve a purpose similar to custom validations for resources and data sources, but with one important difference. The check block is ideal for validations you want to make that should not stop a plan and apply from finishing. If a check fails the deployment will still continue. You will get a warning in the output indicating that the check failed. ([View Highlight] (https://read.readwise.io/read/01hhavj487c8fcc2p5h3w077s8))