test: add empty configuration test scenario

Author: bruzina

README.md

@@ -245,8 +245,18 @@ terraform -chdir=terraform plan
 terraform -chdir=terraform apply
 ```
 
+## Development
+
+Format Terraform configuration by `terraform -chdir=terraform fmt -recursive`.
+
 ## Testing
 
+### Terraform Test
+
+Run test scenarios in [`terraform/tests`](terraform/tests/) by `terraform -chdir=terraform test`.
+
+### End-to-end Tessting
+
 This repository is tested using [`test.yaml`](test.yaml) as the configuration file for the [Xebis Test GitHub Organization](https://github.com/xebis-test) settings and repositories.
 
 The workflow is designed to post a Terraform plan as a pull request comment whenever a pull request to the main branch is created or whenever a new commit to the pull request is pushed. Once the pull request is merged into `main`, the plan is applied automatically.

terraform/tests/empty.tftest.hcl

@@ -0,0 +1,12 @@
+run "empty_file" {
+  command = plan
+
+  variables {
+    path = "tests/fixtures/empty.yaml"
+  }
+
+  assert {
+    condition     = local.config == null
+    error_message = "Expected empty file to produce empty result."
+  }
+}

terraform/tests/fixtures/empty.yaml

@@ -0,0 +1 @@
+---