Most beginners assume testing a Terraform module requires deploying infrastructure.
That assumption creates unnecessary cost and hides the real purpose of testing.
A module is not the infrastructure.
A module is the contract between inputs and outputs.
Testing focuses on that contract.
Plan-based tests evaluate how inputs flow through variables, resources, and outputs without creating anything in AWS. Assertions verify that outputs match expected structure. Validation blocks ensure bad input fails early.
This shifts testing from cloud behavior to module correctness.
Apply-based tests still exist, but only when provider-generated values must be verified. Everything else should fail or pass before infrastructure is created.
The result is faster feedback, lower cost, and stronger module interfaces.