Iterating locally using test stages

Most automated tests written with Terratest consist of multiple “stages”, such as:

1. Build an AMI using Packer
2. Deploy the AMI using Terraform
3. Validate that the AMI works as expected
4. Undeploy the AMI using Terraform

Often, while testing locally, you’ll want to re-run some subset of these stages over and over again: for example, you might want to repeatedly run the validation step while you work out the kinks. Having to run all of these stages each time you change a single line of code can be very slow.

This is where Terratest’s test_structure package comes in handy: it allows you to explicitly break up your tests into stages and to be able to disable any one of those stages by setting an environment variable. Check out the terraform_packer_example_test.go for working sample code.

How to skip stages

To skip a stage, set SKIP_<stage_name> to any non-empty value. For example, to re-run deploy and validation without rebuilding the AMI:

SKIP_build_ami=true go test -v -run TestTerraformPackerExample

This works because each stage saves its outputs (AMI IDs, Terraform options, etc.) to the working directory using functions like SaveString and SaveAmiId. Subsequent stages load this cached data using LoadString, LoadAmiId, etc. When any SKIP_* variable is set, Terratest also skips copying to a temp folder, preserving cached state between runs.