| name | terraform-test |
| description | Comprehensive guide for writing and running Terraform tests. Use when creating test files (.tftest.hcl), writing test scenarios with run blocks, validating infrastructure behavior with assertions, mocking providers and data sources, testing module outputs and resource configurations, or troubleshooting Terraform test syntax and execution. Terraform test is typically used when validating Terraform modules. |
Terraform Test
Terraform's built-in testing framework enables module authors to validate that configuration updates don't introduce breaking changes. Tests execute against temporary resources, protecting existing infrastructure and state files.
Core Concepts
Test File: A .tftest.hcl or .tftest.json file containing test configuration and run blocks that validate your Terraform configuration.
Test Block: Optional configuration block that defines test-wide settings (available since Terraform 1.6.0).
Run Block: Defines a single test scenario with optional variables, provider configurations, and assertions. Each test file requires at least one run block.
Assert Block: Contains conditions that must evaluate to true for the test to pass. Failed assertions cause the test to fail.
Mock Provider: Simulates provider behavior without creating real infrastructure (available since Terraform 1.7.0).
Test Modes: Tests run in apply mode (default, creates real infrastructure) or plan mode (validates logic without creating resources).
File Structure
Terraform test files use the .tftest.hcl or .tftest.json extension and are typically organized in a tests/ directory. Use clear naming conventions to distinguish between unit tests (plan mode) and integration tests (apply mode):
my-module/
├── main.tf
├── variables.tf
├── outputs.tf
└── tests/
├── validation_unit_test.tftest.hcl # Unit test (plan mode)
├── edge_cases_unit_test.tftest.hcl # Unit test (plan mode)
└── full_stack_integration_test.tftest.hcl # Integration test (apply mode - creates real resources)
Test File Components
A test file contains:
- Zero to one
test block (configuration settings)
- One to many
run blocks (test executions)
- Zero to one
variables block (input values)
- Zero to many
provider blocks (provider configuration)
- Zero to many
mock_provider blocks (mock provider data, since v1.7.0)
Important: The order of variables and provider blocks doesn't matter. Terraform processes all values within these blocks at the beginning of the test operation.
Test Configuration (.tftest.hcl)
Test Block
The optional test block configures test-wide settings:
test {
parallel = true # Enable parallel execution for all run blocks (default: false)
}
Test Block Attributes:
parallel - Boolean, when set to true, enables parallel execution for all run blocks by default (default: false). Individual run blocks can override this setting.
Run Block
Each run block executes a command against your configuration. Run blocks execute sequentially by default.
Basic Integration Test (Apply Mode - Default):
run "test_instance_creation" {
command = apply
assert {
condition = aws_instance.example.id != ""
error_message = "Instance should be created with a valid ID"
}
assert {
condition = output.instance_public_ip != ""
error_message = "Instance should have a public IP"
}
}
Unit Test (Plan Mode):
run "test_default_configuration" {
command = plan
assert {
condition = aws_instance.example.instance_type == "t2.micro"
error_message = "Instance type should be t2.micro by default"
}
assert {
condition = aws_instance.example.tags["Environment"] == "test"
error_message = "Environment tag should be 'test'"
}
}
Run Block Attributes:
command - Either apply (default) or planplan_options - Configure plan behavior (see below)variables - Override test-level variable valuesmodule - Reference alternate modules for testingproviders - Customize provider availabilityassert - Validation conditions (multiple allowed)expect_failures - Specify expected validation failuresstate_key - Manage state file isolation (since v1.9.0)parallel - Enable parallel execution when set to true (since v1.9.0)
Plan Options
The plan_options block configures plan command behavior:
run "test_refresh_only" {
command = plan
plan_options {
mode = refresh-only # "normal" (default) or "refresh-only"
refresh = true # boolean, defaults to true
replace = [
aws_instance.example
]
target = [
aws_instance.example
]
}
assert {
condition = aws_instance.example.instance_type == "t2.micro"
error_message = "Instance type should be t2.micro"
}
}
Plan Options Attributes:
mode - normal (default) or refresh-onlyrefresh - Boolean, defaults to truereplace - List of resource addresses to replacetarget - List of resource addresses to target
Variables Block
Define variables at the test file level (applied to all run blocks) or within individual run blocks.
Important: Variables defined in test files take the highest precedence, overriding environment variables, variables files, or command-line input.
File-Level Variables:
# Applied to all run blocks
variables {
aws_region = "us-west-2"
instance_type = "t2.micro"
environment = "test"
}
run "test_with_file_variables" {
command = plan
assert {
condition = var.aws_region == "us-west-2"
error_message = "Region should be us-west-2"
}
}
Run Block Variables (Override File-Level):
variables {
instance_type = "t2.small"
environment = "test"
}
run "test_with_override_variables" {
command = plan
# Override file-level variables
variables {
instance_type = "t3.large"
}
assert {
condition = var.instance_type == "t3.large"
error_message = "Instance type should be overridden to t3.large"
}
}
Variables Referencing Prior Run Blocks:
run "setup_vpc" {
command = apply
}
run "test_with_vpc_output" {
command = plan
variables {
vpc_id = run.setup_vpc.vpc_id
}
assert {
condition = var.vpc_id == run.setup_vpc.vpc_id
error_message = "VPC ID should match setup_vpc output"
}
}
Assert Block
Assert blocks validate conditions within run blocks. All assertions must pass for the test to succeed.
Syntax:
assert {
condition = <expression>
error_message = "failure description"
}
Resource Attribute Assertions:
run "test_resource_configuration" {
command = plan
assert {
condition = aws_s3_bucket.example.bucket == "my-test-bucket"
error_message = "Bucket name should match expected value"
}
assert {
condition = aws_s3_bucket.example.versioning[0].enabled == true
error_message = "Bucket versioning should be enabled"
}
assert {
condition = length(aws_s3_bucket.example.tags) > 0
error_message = "Bucket should have at least one tag"
}
}
Output Validation:
run "test_outputs" {
command = plan
assert {
condition = output.vpc_id != ""
error_message = "VPC ID output should not be empty"
}
assert {
condition = length(output.subnet_ids) == 3
error_message = "Should create exactly 3 subnets"
}
}
Referencing Prior Run Block Outputs:
run "create_vpc" {
command = apply
}
run "validate_vpc_output" {
command = plan
assert {
condition = run.create_vpc.vpc_id != ""
error_message = "VPC from previous run should have an ID"
}
}
Complex Conditions:
run "test_complex_validation" {
command = plan
assert {
condition = alltrue([
for subnet in aws_subnet.private :
can(regex("^10\\.0\\.", subnet.cidr_block))
])
error_message = "All private subnets should use 10.0.0.0/8 CIDR range"
}
assert {
condition = alltrue([
for instance in aws_instance.workers :
contains(["t2.micro", "t2.small", "t3.micro"], instance.instance_type)
])
error_message = "Worker instances should use approved instance types"
}
}
Expect Failures Block
Test that certain conditions intentionally fail. The test passes if the specified checkable objects report an issue, and fails if they do not.
Checkable objects include: Input variables, output values, check blocks, and managed resources or data sources.
run "test_invalid_input_rejected" {
command = plan
variables {
instance_count = -1
}
expect_failures = [
var.instance_count
]
}
Testing Custom Conditions:
run "test_custom_condition_failure" {
command = plan
variables {
instance_type = "t2.nano" # Invalid type
}
expect_failures = [
var.instance_type
]
}
Module Block
Test a specific module rather than the root configuration.
Supported Module Sources:
- ✅ Local modules:
./modules/vpc, ../shared/networking
- ✅ Public Terraform Registry:
terraform-aws-modules/vpc/aws
- ✅ Private Registry (HCP Terraform):
app.terraform.io/org/module/provider
Unsupported Module Sources:
- ❌ Git repositories:
git::https://github.com/...
- ❌ HTTP URLs:
https://example.com/module.zip
- ❌ Other remote sources (S3, GCS, etc.)
Module Block Attributes:
source - Module source (local path or registry address)version - Version constraint (only for registry modules)
Testing Local Modules:
run "test_vpc_module" {
command = plan
module {
source = "./modules/vpc"
}
variables {
cidr_block = "10.0.0.0/16"
name = "test-vpc"
}
assert {
condition = aws_vpc.main.cidr_block == "10.0.0.0/16"
error_message = "VPC CIDR should match input variable"
}
}
Testing Public Registry Modules:
run "test_registry_module" {
command = plan
module {
source = "terraform-aws-modules/vpc/aws"
version = "5.0.0"
}
variables {
name = "test-vpc"
cidr = "10.0.0.0/16"
}
assert {
condition = output.vpc_id != ""
error_message = "VPC should be created"
}
}
Provider Configuration
Override or configure providers for tests. Since Terraform 1.7.0, provider blocks can reference test variables and prior run block outputs.
Basic Provider Configuration:
provider "aws" {
region = "us-west-2"
}
run "test_with_provider" {
command = plan
assert {
condition = aws_instance.example.availability_zone == "us-west-2a"
error_message = "Instance should be in us-west-2 region"
}
}
Multiple Provider Configurations:
provider "aws" {
alias = "primary"
region = "us-west-2"
}
provider "aws" {
alias = "secondary"
region = "us-east-1"
}
run "test_with_specific_provider" {
command = plan
providers = {
aws = provider.aws.secondary
}
assert {
condition = aws_instance.example.availability_zone == "us-east-1a"
error_message = "Instance should be in us-east-1 region"
}
}
Provider with Test Variables:
variables {
aws_region = "eu-west-1"
}
provider "aws" {
region = var.aws_region
}
State Key Management
The state_key attribute controls which state file a run block uses. By default:
- The main configuration shares a state file across all run blocks
- Each alternate module (referenced via
module block) gets its own state file
Force Run Blocks to Share State:
run "create_vpc" {
command = apply
module {
source = "./modules/vpc"
}
state_key = "shared_state"
}
run "create_subnet" {
command = apply
module {
source = "./modules/subnet"
}
state_key = "shared_state" # Shares state with create_vpc
}
Parallel Execution
Run blocks execute sequentially by default. Enable parallel execution with parallel = true.
Requirements for Parallel Execution:
- No inter-run output references (run blocks cannot reference outputs from parallel runs)
- Different state files (via different modules or state keys)
- Explicit
parallel = true attribute
run "test_module_a" {
command = plan
parallel = true
module {
source = "./modules/module-a"
}
assert {
condition = output.result != ""
error_message = "Module A should produce output"
}
}
run "test_module_b" {
command = plan
parallel = true
module {
source = "./modules/module-b"
}
assert {
condition = output.result != ""
error_message = "Module B should produce output"
}
}
# This creates a synchronization point
run "test_integration" {
command = plan
# Waits for parallel runs above to complete
assert {
condition = output.combined != ""
error_message = "Integration should work"
}
}
Mock Providers
Mock providers simulate provider behavior without creating real infrastructure (available since Terraform 1.7.0).
Basic Mock Provider:
mock_provider "aws" {
mock_resource "aws_instance" {
defaults = {
id = "i-1234567890abcdef0"
instance_type = "t2.micro"
ami = "ami-12345678"
}
}
mock_data "aws_ami" {
defaults = {
id = "ami-12345678"
}
}
}
run "test_with_mocks" {
command = plan
assert {
condition = aws_instance.example.id == "i-1234567890abcdef0"
error_message = "Mock instance ID should match"
}
}
Advanced Mock with Custom Values:
mock_provider "aws" {
alias = "mocked"
mock_resource "aws_s3_bucket" {
defaults = {
id = "test-bucket-12345"
bucket = "test-bucket"
arn = "arn:aws:s3:::test-bucket"
}
}
mock_data "aws_availability_zones" {
defaults = {
names = ["us-west-2a", "us-west-2b", "us-west-2c"]
}
}
}
run "test_with_mock_provider" {
command = plan
providers = {
aws = provider.aws.mocked
}
assert {
condition = length(data.aws_availability_zones.available.names) == 3
error_message = "Should return 3 availability zones"
}
}
Test Execution
Running Tests
Run all tests:
terraform test
Run specific test file:
terraform test tests/defaults.tftest.hcl
Run with verbose output:
terraform test -verbose
Run tests in a specific directory:
terraform test -test-directory=integration-tests
Filter tests by name:
terraform test -filter=test_vpc_configuration
Run tests without cleanup (for debugging):
terraform test -no-cleanup
Test Output
Successful test output:
tests/defaults.tftest.hcl... in progress
run "test_default_configuration"... pass
run "test_outputs"... pass
tests/defaults.tftest.hcl... tearing down
tests/defaults.tftest.hcl... pass
Success! 2 passed, 0 failed.
Failed test output:
tests/defaults.tftest.hcl... in progress
run "test_default_configuration"... fail
Error: Test assertion failed
Instance type should be t2.micro by default
Success! 0 passed, 1 failed.
Common Test Patterns (Unit Tests - Plan Mode)
The following examples demonstrate common unit test patterns using command = plan. These tests validate Terraform logic without creating real infrastructure, making them fast and cost-free.
Testing Module Outputs
run "test_module_outputs" {
command = plan
assert {
condition = output.vpc_id != null
error_message = "VPC ID output must be defined"
}
assert {
condition = can(regex("^vpc-", output.vpc_id))
error_message = "VPC ID should start with 'vpc-'"
}
assert {
condition = length(output.subnet_ids) >= 2
error_message = "Should output at least 2 subnet IDs"
}
}
Testing Resource Counts
run "test_resource_count" {
command = plan
variables {
instance_count = 3
}
assert {
condition = length(aws_instance.workers) == 3
error_message = "Should create exactly 3 worker instances"
}
}
Testing Conditional Resources
run "test_conditional_resource_created" {
command = plan
variables {
create_nat_gateway = true
}
assert {
condition = length(aws_nat_gateway.main) == 1
error_message = "NAT gateway should be created when enabled"
}
}
run "test_conditional_resource_not_created" {
command = plan
variables {
create_nat_gateway = false
}
assert {
condition = length(aws_nat_gateway.main) == 0
error_message = "NAT gateway should not be created when disabled"
}
}
Testing Tags
run "test_resource_tags" {
command = plan
variables {
common_tags = {
Environment = "production"
ManagedBy = "Terraform"
}
}
assert {
condition = aws_instance.example.tags["Environment"] == "production"
error_message = "Environment tag should be set correctly"
}
assert {
condition = aws_instance.example.tags["ManagedBy"] == "Terraform"
error_message = "ManagedBy tag should be set correctly"
}
}
Sequential Tests with Dependencies
run "setup_vpc" {
# command defaults to apply
variables {
vpc_cidr = "10.0.0.0/16"
}
assert {
condition = output.vpc_id != ""
error_message = "VPC should be created"
}
}
run "test_subnet_in_vpc" {
command = plan
variables {
vpc_id = run.setup_vpc.vpc_id
}
assert {
condition = aws_subnet.example.vpc_id == run.setup_vpc.vpc_id
error_message = "Subnet should be created in the VPC from setup_vpc"
}
}
Testing Data Sources
run "test_data_source_lookup" {
command = plan
assert {
condition = data.aws_ami.ubuntu.id != ""
error_message = "Should find a valid Ubuntu AMI"
}
assert {
condition = can(regex("^ami-", data.aws_ami.ubuntu.id))
error_message = "AMI ID should be in correct format"
}
}
Testing Validation Rules
# In variables.tf
variable "environment" {
type = string
validation {
condition = contains(["dev", "staging", "prod"], var.environment)
error_message = "Environment must be dev, staging, or prod"
}
}
# In test file
run "test_valid_environment" {
command = plan
variables {
environment = "staging"
}
assert {
condition = var.environment == "staging"
error_message = "Valid environment should be accepted"
}
}
run "test_invalid_environment" {
command = plan
variables {
environment = "invalid"
}
expect_failures = [
var.environment
]
}
Integration Testing
For tests that create real infrastructure (default behavior with command = apply):
run "integration_test_full_stack" {
# command defaults to apply
variables {
environment = "integration-test"
vpc_cidr = "10.100.0.0/16"
}
assert {
condition = aws_vpc.main.id != ""
error_message = "VPC should be created"
}
assert {
condition = length(aws_subnet.private) == 2
error_message = "Should create 2 private subnets"
}
assert {
condition = aws_instance.bastion.public_ip != ""
error_message = "Bastion instance should have a public IP"
}
}
# Cleanup happens automatically after test completes
Cleanup and Destruction
Important: Resources are destroyed in reverse run block order after test completion. This is critical for configurations with dependencies.
Example: For S3 buckets containing objects, the bucket must be emptied before deletion:
run "create_bucket_with_objects" {
command = apply
assert {
condition = aws_s3_bucket.example.id != ""
error_message = "Bucket should be created"
}
}
run "add_objects_to_bucket" {
command = apply
assert {
condition = length(aws_s3_object.files) > 0
error_message = "Objects should be added"
}
}
# Cleanup occurs in reverse order:
# 1. Destroys objects (run "add_objects_to_bucket")
# 2. Destroys bucket (run "create_bucket_with_objects")
Disable Cleanup for Debugging:
terraform test -no-cleanup
Best Practices
-
Test Organization: Organize tests by type using clear naming conventions:
- Unit tests (plan mode):
*_unit_test.tftest.hcl - fast, no resources created
- Integration tests (apply mode):
*_integration_test.tftest.hcl - creates real resources
- Example:
defaults_unit_test.tftest.hcl, validation_unit_test.tftest.hcl, full_stack_integration_test.tftest.hcl
- This makes it easy to run unit tests separately from integration tests in CI/CD
-
Apply vs Plan:
- Default is
command = apply (integration testing with real resources)
- Use
command = plan for unit tests (fast, no real resources)
- Use mocks for isolated unit testing
-
Meaningful Assertions: Write clear, specific assertion error messages that help diagnose failures
-
Test Isolation: Each run block should be independent when possible. Use sequential runs only when testing dependencies
-
Variable Coverage: Test different variable combinations to validate all code paths. Remember that test variables have the highest precedence
-
Mock Providers: Use mocks for external dependencies to speed up tests and reduce costs (requires Terraform 1.7.0+)
-
Cleanup: Integration tests automatically destroy resources in reverse order after completion. Use -no-cleanup flag for debugging
-
CI Integration: Run terraform test in CI/CD pipelines to catch issues early
-
Test Naming: Use descriptive names for run blocks that explain what scenario is being tested
-
Negative Testing: Test invalid inputs and expected failures using expect_failures
-
Module Support: Remember that test files only support local and registry modules, not Git or other sources
-
Parallel Execution: Use parallel = true for independent tests with different state files to speed up test execution
Advanced Features
Testing with Refresh-Only Mode
run "test_refresh_only" {
command = plan
plan_options {
mode = refresh-only
}
assert {
condition = aws_instance.example.tags["Environment"] == "production"
error_message = "Tags should be refreshed correctly"
}
}
Testing with Targeted Resources
run "test_specific_resource" {
command = plan
plan_options {
target = [
aws_instance.example
]
}
assert {
condition = aws_instance.example.instance_type == "t2.micro"
error_message = "Targeted resource should be planned"
}
}
Testing Multiple Modules in Parallel
run "test_networking_module" {
command = plan
parallel = true
module {
source = "./modules/networking"
}
variables {
cidr_block = "10.0.0.0/16"
}
assert {
condition = output.vpc_id != ""
error_message = "VPC should be created"
}
}
run "test_compute_module" {
command = plan
parallel = true
module {
source = "./modules/compute"
}
variables {
instance_type = "t2.micro"
}
assert {
condition = output.instance_id != ""
error_message = "Instance should be created"
}
}
Custom State Management
run "create_foundation" {
command = apply
state_key = "foundation"
assert {
condition = aws_vpc.main.id != ""
error_message = "Foundation VPC should be created"
}
}
run "create_application" {
command = apply
state_key = "foundation" # Share state with foundation
variables {
vpc_id = run.create_foundation.vpc_id
}
assert {
condition = aws_instance.app.vpc_id == run.create_foundation.vpc_id
error_message = "Application should use foundation VPC"
}
}
Troubleshooting
Test Failures
Issue: Assertion failures
Solution: Review error messages, check actual vs expected values, verify variable inputs. Use -verbose flag for detailed output
Provider Authentication
Issue: Tests fail due to missing credentials
Solution: Configure provider credentials for testing, or use mock providers for unit tests (available since v1.7.0)
Resource Dependencies
Issue: Tests fail due to missing dependencies
Solution: Use sequential run blocks or create setup runs to establish required resources. Remember cleanup happens in reverse order
Long Test Execution
Issue: Tests take too long to run
Solution:
- Use
command = plan instead of apply where possible
- Leverage mock providers
- Use
parallel = true for independent tests
- Organize slow integration tests separately
State Conflicts
Issue: Multiple tests interfere with each other
Solution:
- Use different modules (automatic separate state)
- Use
state_key attribute to control state file sharing
- Use mock providers for isolated testing
Module Source Errors
Issue: Test fails with unsupported module source
Solution: Terraform test files only support local and registry modules. Convert Git or HTTP sources to local modules or use registry modules
Example Test Suite
Complete example testing a VPC module, demonstrating both unit tests (plan mode) and integration tests (apply mode):
# tests/vpc_module_unit_test.tftest.hcl
# This file contains unit tests using command = plan (fast, no resources created)
variables {
environment = "test"
aws_region = "us-west-2"
}
# ============================================================================
# UNIT TESTS (Plan Mode) - Validate logic without creating resources
# ============================================================================
# Test default configuration
run "test_defaults" {
command = plan
variables {
vpc_cidr = "10.0.0.0/16"
vpc_name = "test-vpc"
}
assert {
condition = aws_vpc.main.cidr_block == "10.0.0.0/16"
error_message = "VPC CIDR should match input"
}
assert {
condition = aws_vpc.main.enable_dns_hostnames == true
error_message = "DNS hostnames should be enabled by default"
}
assert {
condition = aws_vpc.main.tags["Name"] == "test-vpc"
error_message = "VPC name tag should match input"
}
}
# Test subnet creation
run "test_subnets" {
command = plan
variables {
vpc_cidr = "10.0.0.0/16"
vpc_name = "test-vpc"
public_subnets = ["10.0.1.0/24", "10.0.2.0/24"]
private_subnets = ["10.0.10.0/24", "10.0.11.0/24"]
}
assert {
condition = length(aws_subnet.public) == 2
error_message = "Should create 2 public subnets"
}
assert {
condition = length(aws_subnet.private) == 2
error_message = "Should create 2 private subnets"
}
assert {
condition = alltrue([
for subnet in aws_subnet.private :
subnet.map_public_ip_on_launch == false
])
error_message = "Private subnets should not assign public IPs"
}
}
# Test outputs
run "test_outputs" {
command = plan
variables {
vpc_cidr = "10.0.0.0/16"
vpc_name = "test-vpc"
}
assert {
condition = output.vpc_id != ""
error_message = "VPC ID output should not be empty"
}
assert {
condition = can(regex("^vpc-", output.vpc_id))
error_message = "VPC ID should have correct format"
}
assert {
condition = output.vpc_cidr == "10.0.0.0/16"
error_message = "VPC CIDR output should match input"
}
}
# Test invalid CIDR block
run "test_invalid_cidr" {
command = plan
variables {
vpc_cidr = "invalid"
vpc_name = "test-vpc"
}
expect_failures = [
var.vpc_cidr
]
}
# tests/vpc_module_integration_test.tftest.hcl
# This file contains integration tests using command = apply (creates real resources)
variables {
environment = "integration-test"
aws_region = "us-west-2"
}
# ============================================================================
# INTEGRATION TESTS (Apply Mode) - Creates and validates real infrastructure
# ============================================================================
# Integration test creating real VPC
run "integration_test_vpc_creation" {
# command defaults to apply - creates real AWS resources!
variables {
vpc_cidr = "10.100.0.0/16"
vpc_name = "integration-test-vpc"
}
assert {
condition = aws_vpc.main.id != ""
error_message = "VPC should be created with valid ID"
}
assert {
condition = aws_vpc.main.state == "available"
error_message = "VPC should be in available state"
}
}
# tests/vpc_module_mock_test.tftest.hcl
# This file demonstrates mock provider testing - fastest option, no credentials needed
# ============================================================================
# MOCK TESTS (Plan Mode with Mocks) - No real infrastructure or API calls
# ============================================================================
# Mock tests are ideal for:
# - Testing complex logic without cloud costs
# - Running tests without provider credentials
# - Fast feedback in local development
# - CI/CD pipelines without cloud access
# - Testing with predictable data source results
# Define mock provider to simulate AWS behavior
mock_provider "aws" {
# Mock EC2 instances - returns these values instead of creating real resources
mock_resource "aws_instance" {
defaults = {
id = "i-1234567890abcdef0"
arn = "arn:aws:ec2:us-west-2:123456789012:instance/i-1234567890abcdef0"
instance_type = "t2.micro"
ami = "ami-12345678"
availability_zone = "us-west-2a"
subnet_id = "subnet-12345678"
vpc_security_group_ids = ["sg-12345678"]
associate_public_ip_address = true
public_ip = "203.0.113.1"
private_ip = "10.0.1.100"
tags = {}
}
}
# Mock VPC resources
mock_resource "aws_vpc" {
defaults = {
id = "vpc-12345678"
arn = "arn:aws:ec2:us-west-2:123456789012:vpc/vpc-12345678"
cidr_block = "10.0.0.0/16"
enable_dns_hostnames = true
enable_dns_support = true
instance_tenancy = "default"
tags = {}
}
}
# Mock subnet resources
mock_resource "aws_subnet" {
defaults = {
id = "subnet-12345678"
arn = "arn:aws:ec2:us-west-2:123456789012:subnet/subnet-12345678"
vpc_id = "vpc-12345678"
cidr_block = "10.0.1.0/24"
availability_zone = "us-west-2a"
map_public_ip_on_launch = false
tags = {}
}
}
# Mock S3 bucket resources
mock_resource "aws_s3_bucket" {
defaults = {
id = "test-bucket-12345"
arn = "arn:aws:s3:::test-bucket-12345"
bucket = "test-bucket-12345"
bucket_domain_name = "test-bucket-12345.s3.amazonaws.com"
region = "us-west-2"
tags = {}
}
}
# Mock data sources - critical for testing modules that query existing infrastructure
mock_data "aws_ami" {
defaults = {
id = "ami-0c55b159cbfafe1f0"
name = "ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-20210430"
architecture = "x86_64"
root_device_type = "ebs"
virtualization_type = "hvm"
owners = ["099720109477"]
}
}
mock_data "aws_availability_zones" {
defaults = {
names = ["us-west-2a", "us-west-2b", "us-west-2c"]
zone_ids = ["usw2-az1", "usw2-az2", "usw2-az3"]
}
}
mock_data "aws_vpc" {
defaults = {
id = "vpc-12345678"
cidr_block = "10.0.0.0/16"
enable_dns_hostnames = true
enable_dns_support = true
}
}
}
# Test 1: Validate resource configuration with mocked values
run "test_instance_with_mocks" {
command = plan # Mocks only work with plan mode
variables {
instance_type = "t2.micro"
ami_id = "ami-12345678"
}
assert {
condition = aws_instance.example.instance_type == "t2.micro"
error_message = "Instance type should match input variable"
}
assert {
condition = aws_instance.example.id == "i-1234567890abcdef0"
error_message = "Mock should return consistent instance ID"
}
assert {
condition = can(regex("^203\\.0\\.113\\.", aws_instance.example.public_ip))
error_message = "Mock public IP should be in TEST-NET-3 range"
}
}
# Test 2: Validate data source behavior with mocked results
run "test_data_source_with_mocks" {
command = plan
assert {
condition = data.aws_ami.ubuntu.id == "ami-0c55b159cbfafe1f0"
error_message = "Mock data source should return predictable AMI ID"
}
assert {
condition = length(data.aws_availability_zones.available.names) == 3
error_message = "Should return 3 mocked availability zones"
}
assert {
condition = contains(
data.aws_availability_zones.available.names,
"us-west-2a"
)
error_message = "Should include us-west-2a in mocked zones"
}
}
# Test 3: Validate complex logic with for_each and mocks
run "test_multiple_subnets_with_mocks" {
command = plan
variables {
subnet_cidrs = {
"public-a" = "10.0.1.0/24"
"public-b" = "10.0.2.0/24"
"private-a" = "10.0.10.0/24"
"private-b" = "10.0.11.0/24"
}
}
# Test that all subnets are created
assert {
condition = length(keys(aws_subnet.subnets)) == 4
error_message = "Should create 4 subnets from for_each map"
}
# Test that public subnets have correct naming
assert {
condition = alltrue([
for name, subnet in aws_subnet.subnets :
can(regex("^public-", name)) ? subnet.map_public_ip_on_launch == true : true
])
error_message = "Public subnets should map public IPs on launch"
}
# Test that all subnets belong to mocked VPC
assert {
condition = alltrue([
for subnet in aws_subnet.subnets :
subnet.vpc_id == "vpc-12345678"
])
error_message = "All subnets should belong to mocked VPC"
}
}
# Test 4: Validate output values with mocks
run "test_outputs_with_mocks" {
command = plan
assert {
condition = output.vpc_id == "vpc-12345678"
error_message = "VPC ID output should match mocked value"
}
assert {
condition = can(regex("^vpc-", output.vpc_id))
error_message = "VPC ID output should have correct format"
}
assert {
condition = output.instance_public_ip == "203.0.113.1"
error_message = "Instance public IP should match mock"
}
}
# Test 5: Test conditional logic with mocks
run "test_conditional_resources_with_mocks" {
command = plan
variables {
create_bastion = true
create_nat_gateway = false
}
assert {
condition = length(aws_instance.bastion) == 1
error_message = "Bastion should be created when enabled"
}
assert {
condition = length(aws_nat_gateway.nat) == 0
error_message = "NAT gateway should not be created when disabled"
}
}
# Test 6: Test tag propagation with mocks
run "test_tag_inheritance_with_mocks" {
command = plan
variables {
common_tags = {
Environment = "test"
ManagedBy = "Terraform"
Project = "MockTesting"
}
}
# Verify tags are properly merged with defaults
assert {
condition = alltrue([
for key in keys(var.common_tags) :
contains(keys(aws_instance.example.tags), key)
])
error_message = "All common tags should be present on instance"
}
assert {
condition = aws_instance.example.tags["Environment"] == "test"
error_message = "Environment tag should be set correctly"
}
}
# Test 7: Test validation rules with mocks (expect_failures)
run "test_invalid_cidr_with_mocks" {
command = plan
variables {
vpc_cidr = "192.168.0.0/8" # Invalid - should be /16 or /24
}
# Expect custom validation to fail
expect_failures = [
var.vpc_cidr
]
}
# Test 8: Sequential mock tests with state sharing
run "setup_vpc_with_mocks" {
command = plan
variables {
vpc_cidr = "10.0.0.0/16"
vpc_name = "test-vpc"
}
assert {
condition = aws_vpc.main.cidr_block == "10.0.0.0/16"
error_message = "VPC CIDR should match input"
}
}
run "test_subnet_references_vpc_with_mocks" {
command = plan
variables {
vpc_id = run.setup_vpc_with_mocks.vpc_id
subnet_cidr = "10.0.1.0/24"
}
assert {
condition = aws_subnet.example.vpc_id == run.setup_vpc_with_mocks.vpc_id
error_message = "Subnet should reference VPC from previous run"
}
assert {
condition = aws_subnet.example.vpc_id == "vpc-12345678"
error_message = "VPC ID should match mocked value"
}
}
Key Benefits of Mock Testing:
- No Cloud Costs: Runs entirely locally without creating infrastructure
- No Credentials Needed: Perfect for CI/CD environments without cloud access
- Fast Execution: Tests complete in seconds, not minutes
- Predictable Results: Data sources return consistent values
- Isolated Testing: No dependencies on existing cloud resources
- Safe Experimentation: Test destructive operations without risk
Limitations of Mock Testing:
- Plan Mode Only: Mocks don't work with
command = apply
- Not Real Behavior: Mocks may not reflect actual provider API behavior
- Computed Values: Mock defaults may not match real computed attributes
- Provider Updates: Mocks need manual updates when provider schemas change
- Resource Interactions: Can't test real resource dependencies or timing issues
When to Use Mock Tests:
- ✅ Testing Terraform logic and conditionals
- ✅ Validating variable transformations
- ✅ Testing for_each and count expressions
- ✅ Checking output calculations
- ✅ Local development without cloud access
- ✅ Fast CI/CD feedback loops
- ❌ Validating actual provider behavior
- ❌ Testing real resource creation side effects
- ❌ Verifying API-level interactions
- ❌ End-to-end integration testing
CI/CD Integration
GitHub Actions Example
name: Terraform Tests
on:
pull_request:
branches: [ main ]
push:
branches: [ main ]
jobs:
terraform-test:
runs-on: ubuntu-latest
steps:
- name: Checkout code
uses: actions/checkout@v4
- name: Setup Terraform
uses: hashicorp/setup-terraform@v3
with:
terraform_version: 1.9.0
- name: Terraform Format Check
run: terraform fmt -check -recursive
- name: Terraform Init
run: terraform init
- name: Terraform Validate
run: terraform validate
- name: Run Terraform Tests
run: terraform test -verbose
env:
AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
GitLab CI Example
terraform-test:
image: hashicorp/terraform:1.9
stage: test
before_script:
- terraform init
script:
- terraform fmt -check -recursive
- terraform validate
- terraform test -verbose
only:
- merge_requests
- main
References
For more information:
