Terraform Test Skill

Write, organize, and run Terraform's built-in test framework for Azure infrastructure modules.

Reference: Terraform Testing Documentation

Quick Reference

File Structure

my-module/
├── main.tf
├── variables.tf
├── outputs.tf
└── tests/
    ├── defaults_unit_test.tftest.hcl        # Plan mode (fast)
    ├── validation_unit_test.tftest.hcl      # Plan mode (fast)
    └── full_stack_integration_test.tftest.hcl  # Apply mode (creates resources)

Naming convention: *_unit_test.tftest.hcl (plan mode), *_integration_test.tftest.hcl (apply mode).

Test File Components

• 0–1 test block (test-wide settings)
• 1+ run blocks (test scenarios, sequential by default)
• 0–1 variables block (file-level inputs, highest precedence)
• 0+ provider blocks (provider configuration)
• 0+ mock_provider blocks (simulated providers, TF 1.7+)

Canonical Example

See references/test-examples.md for a complete Azure Resource Group test (unit tests, tag validation, expect_failures).

Key Syntax Rules

Run Block Attributes

Assert Syntax

assert {
  condition     = <boolean expression>
  error_message = "Human-readable failure description"
}

Assertions can reference: resource attributes, outputs, run.<name>.<output>, var.*, data sources. Variables precedence: run-block > file-level > all other sources. See references/test-examples.md for module blocks, plan options, and prior run references.

Mock Providers (TF 1.7+)

Simulate Azure provider without API calls — ideal for unit tests. Use mock_provider "azurerm" with mock_resource and mock_data blocks. When to use: Unit tests, CI without Azure credentials, fast local development. When NOT to use: Integration tests, validating actual Azure API behavior. See references/mock-providers.md for full mock patterns and examples.

Common Test Patterns

See references/test-examples.md for: conditional resources, tag validation, resource count with for_each, variables precedence, and prior run references.

Running Tests

terraform test                              # All tests
terraform test tests/defaults.tftest.hcl    # Specific file
terraform test -verbose                     # Detailed output
terraform test -filter=test_resource_group  # Filter by name
terraform test -no-cleanup                  # Debug: keep resources

Best Practices

1. Naming: *_unit_test.tftest.hcl / *_integration_test.tftest.hcl
2. Plan mode first: Use command = plan for fast, cost-free validation
3. Clear error messages: Describe what went wrong and expected state
4. Test isolation: Independent run blocks where possible
5. Variable coverage: Test multiple combinations for all code paths
6. Mock for speed: Use mock providers in CI without Azure access
7. Negative testing: Use expect_failures for validation rule coverage
8. Sequential only when needed: Only chain run blocks via run.<name> when required

Terraform MCP Integration

Use mcp_terraform_search_providers to validate that resource types used in test assertions exist in the target provider version.

Reference Index