TopolearnShared modules are code that many teams depend on; they need automated tests too.
terraform test runs test files (*.tftest.hcl, in the module root or tests/). Each file contains run blocks executed in order:
command = planchecks the plan only: fast and needs no real infrastructure for many assertions.command = apply(the default) actually creates the resources, runs assertions, and destroys everything at the end of the file.variables { ... }at file or run level set inputs.assert { condition = ... error_message = ... }blocks check outputs and resource attributes, e.g.aws_s3_bucket.this.bucket == "acme-logs".expect_failures = [var.env]asserts that validation rejects bad input: test your error paths.module { source = "./tests/setup" }in a run block uses a helper module, for example to create prerequisites or to load a fixture.
Mocking (mock_provider "aws" {} in a test file) replaces a provider with one that returns fake values, so even apply-style tests run in seconds without credentials. Combine: unit-style tests with mocks on every commit, real-apply integration tests nightly in a sandbox account.
Run with terraform test, or terraform test -filter=tests/naming.tftest.hcl for one file. Results print pass/fail per run block.
Terratest (Go) remains an option for complex end-to-end checks, such as making HTTP requests to what you deployed.
Example
# tests/bucket.tftest.hcl (module from the modules lesson)
mock_provider "aws" {}
variables {
name = "acme-logs-test"
}
run "versioning_enabled_by_default" {
command = plan
assert {
condition = aws_s3_bucket_versioning.this.versioning_configuration[0].status == "Enabled"
error_message = "Versioning should default to Enabled"
}
}
run "can_disable_versioning" {
variables { versioning = false }
assert {
condition = aws_s3_bucket_versioning.this.versioning_configuration[0].status == "Suspended"
error_message = "versioning = false should suspend versioning"
}
}
# terraform test
# tests/bucket.tftest.hcl... pass (2 passed, 0 failed)Remember
- run blocks with command = plan or apply, plus assert blocks
- expect_failures tests validation errors
- mock_provider makes tests fast and credential-free
Watch out for
- Running apply-mode tests in a production account; use a sandbox, since tests create real resources.