benmarsden / tdd-infra-demo

A demo showcasing some examples of Test-Driven Development (TDD) for Infrastructure

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This repository aims to summarise, in a interactive way, the options available when testing infrastructure code.

It can be 'played' in one of two ways:

  1. For those who prefer a walkthrough, follow the 'Walkthrough' section.
  2. For those who prefer to learn by doing, read the 'Mission' section for a TDD adventure.

Testing tools

1. In this demo

  • terratest: Go library for writing automated tests for your terraform code.
  • terraform-compliance: BDD for terraform.
  • Open Policy Agent: general-purpose policy engine that allows you to create enforceable policies across terraform, k8s resources and more!
  • conftest: Write tests against Open Policy Agent policies
  • pre-commit: runs terraform-fmt, terraform-validate, tflint, golint and gofmt prior to every commit.

2. Outside scope of demo (but interesting)


  • Google Cloud project with billing configured
    • provide the project name and project ID as variables (either by passing them as -var or using a .tfvars file)
  • Testing tools defined above
  • make (if you wish to use the Makefile)
  • terraform
  • go


Click here for the walkthrough
  1. Before all else, get yourself set up with pre-commit:
  • brew install pre-commit
  • pre-commit install
  • test setup with make pre-commit
  1. Let's now learn how we can use terraform-compliance to use BDD to test our terraform code. Run make compliance.
  • to use terraform-compliance, we create features and scenarios with the usual given/when/then syntax. See tests/compliance for examples of this.
  • make compliance evaluates our scenarios against a terraform plan and notifies us of any failures.
  • there are 3 failures: incorrect bucket location, incorrect bucket naming and incorrect bucket admin priviledges. Try fixing them and re-running make compliance to verify your fixes.
  1. We can also use OPA's query language, Rego, to create policies for interpreting structured data (in our case a terraform plan, or a terraform configuration file). Run make opa.
  • make opa runs our Rego policies across a terraform plan and returns both the policy results and coverage over the policies.
    • The policies are themselves only assertions, and we can use conftest as a way to run tests against these assertions locally and in CI.
    • Run make conftest-tfplan. This will generate a terraform plan in .json format, evaluate the policies outlined in tests/policy/bucket_admin.rego and test whether the deny[msg] ... defined there is true.
    • Fix the issue by associating with roles/storage.admin of data.google_iam_policy.naughty-admin. What happens when you re-run make conftest-tfplan?
    • As an interesting alternative, run make conftest-tf. This uses conftest to test against the .tf files directly (as opposed to against the terraform plan).
  1. Thought we were done with OPA and conftest? Not quite! We can take conftest even further by writing tests to validate our OPA policies:
  • tests/policy/bucket_admin_test.rego defines the test_is_bucket_policy, which creates a dummy resource to validate the response of the is_bucket_policy function.
  • In this way, we can not only ensure trust in our infrastructure code, but also in the policies applied to it too!
  • Run make conftest-validate to see this in action.
  1. Great, so now we have a bucket that theoretically adheres to our defined policies. To wrap it up, let's learn how to test this is true in practise using Terratest!
  • Run make terratest.
  • This runs the TestBucketCreation Go test in tests/unit/bucket_test.go, which uses the real terraform scripts in infra/project_init with test-specific variables to assert certain attributes about the created bucket are true.
  • Of course, this is a rather mundane example, but it illustrates a powerful aspect of terratest: testing your infrastructure code in a real environment.


Click here for the mission

Defeat Lord Buckethead

The mischevious intergalatic spacelord Lord Buckethead is back! Since his Brexit schenanigans, he's trying to resupply his barbaric bucket army by sneaking his way into your Google Cloud Storage buckets!

Luckily, because of our rigorous infrastructure testing practices, we've identified 3 changes to your terraform files that indicate Lord Buckethead has infiltrated your systems. While we don't know exactly what these are, we do know the following 3 things about this particularly devious intergalactic spacelord:

  1. If he ever hopes to defeat Boris Johnson, Lord Buckethead needs more buckets in the UK.
  2. Any old bucket is not good enough. If Lord Buckethead ever hopes to keep take power, he will need high-ranking buckets to lead his forces well. Keep an eye out for suspiciously named buckets...
  3. In efforts to rebrand, Lord Buckethead may be converting his bucket army to bins. He will surely need certain permissions over your buckets to do this...

Can you fix the issues and restore the integrity of our infrastructure code?

Win condition: make test passes without errors


To help you in your quest:

  • a Makefile has been included to allow you to execute different types of tests. Failing tests from running make compliance and make conftest-tfplan will provide indication as to what Lord Buckethead has modified.
  • tests reside in the tests/* directories.
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A demo showcasing some examples of Test-Driven Development (TDD) for Infrastructure


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