locals

Terraform policy supports locals blocks in test files. These blocks behave like locals blocks in policy files, allowing you to define reusable values within your tests.

Note

This functionality is in beta. Do not use beta features in production environments.

Configuration model

The locals block supports the following configuration:

locals block
- <name> any | repeatable

Complete configuration example

The following example demonstrates a locals block that sets local values, and a resource block that references local values:

tests/example.policytest.hcl

locals {
  common_tags = {
    ManagedBy   = "terraform"
    Environment = "production"
  }
  
  approved_regions = ["us-east-1", "us-west-2"]
  test_vpc_id      = "vpc-12345678"
}

resource "aws_subnet" "public" {
  attrs = {
    vpc_id            = local.test_vpc_id
    cidr_block        = "10.0.1.0/24"
    availability_zone = local.approved_regions[0]
  }
}

Specification

A locals block supports the following configuration.

`name`

Provide a value for the local with the given name. Refer to local values in your policy tests with local.<name>.

Data type: Any
Default: None
Repeatable

Scope

Local values defined in test files are available throughout the test file and can be referenced using the local.<name> syntax.

Examples

The following examples demonstrate common locals block configuration patterns for specific use cases.

Common test data

In the following example, the locals block defines shared test values that multiple resource test cases reference to maintain consistency.

locals {
  test_az     = "us-east-1a"
  test_ami    = "ami-12345678"
}

resource "aws_instance" "example1" {
  attrs = {
    instance_type     = "t3.micro"
    ami               = local.test_ami
    availability_zone = local.test_az
  }
}

resource "aws_instance" "example2" {
  attrs = {
    instance_type     = "t3.small"
    ami               = local.test_ami
    availability_zone = local.test_az
  }
}

Shared tags

In the following example, the locals block defines common tags that multiple resource test cases apply to ensure consistent tagging across resources.

locals {
  common_tags = {
    ManagedBy   = "terraform"
    Environment = "test"
    Owner       = "platform-team"
  }
}

resource "aws_instance" "web" {
  attrs = {
    instance_type = "t3.micro"
    ami           = "ami-12345678"
    tags          = local.common_tags
  }
}

resource "aws_s3_bucket" "data" {
  attrs = {
    bucket = "test-bucket"
    tags   = local.common_tags
  }
}

Complex data structures

In the following example, the locals block defines nested objects and lists that resource test cases use to configure VPC and subnet relationships.

locals {
  vpc_config = {
    id         = "vpc-12345678"
    cidr_block = "10.0.0.0/16"
  }
  
  subnet_configs = [
    {
      cidr_block        = "10.0.1.0/24"
      availability_zone = "us-east-1a"
    },
    {
      cidr_block        = "10.0.2.0/24"
      availability_zone = "us-east-1b"
    }
  ]
}

resource "aws_subnet" "subnet1" {
  attrs = {
    vpc_id            = local.vpc_config.id
    cidr_block        = local.subnet_configs[0].cidr_block
    availability_zone = local.subnet_configs[0].availability_zone
  }
}

resource "aws_subnet" "subnet2" {
  attrs = {
    vpc_id            = local.vpc_config.id
    cidr_block        = local.subnet_configs[1].cidr_block
    availability_zone = local.subnet_configs[1].availability_zone
  }
}

Computed values

In the following example, the locals block uses string interpolation and list comprehensions to generate computed values for resource configurations.

locals {
  base_name = "test"
  vpc_name  = "${local.base_name}-vpc"
  sg_name   = "${local.base_name}-sg"
  
  instance_count = 3
  instance_names = [for i in range(local.instance_count) : "${local.base_name}-instance-${i}"]
}

resource "aws_vpc" "main" {
  attrs = {
    cidr_block = "10.0.0.0/16"
    tags = {
      Name = local.vpc_name
    }
  }
}

resource "aws_security_group" "main" {
  attrs = {
    name        = local.sg_name
    description = "Security group for ${local.base_name}"
  }
}

Reference data sources

In the following example, the locals block references mock data sources to create derived values that resource test cases use for their configurations.

locals {
  vpc_id = data.aws_vpc.main.id
  subnet_ids = [
    data.aws_subnet.private1.id,
    data.aws_subnet.private2.id
  ]
}

data "aws_vpc" "main" {
  attrs = {
    id         = "vpc-12345678"
    cidr_block = "10.0.0.0/16"
  }
}

data "aws_subnet" "private1" {
  attrs = {
    id     = "subnet-12345678"
    vpc_id = local.vpc_id
  }
}

data "aws_subnet" "private2" {
  attrs = {
    id     = "subnet-87654321"
    vpc_id = local.vpc_id
  }
}

resource "aws_instance" "app" {
  attrs = {
    instance_type = "t3.micro"
    ami           = "ami-12345678"
    subnet_id     = local.subnet_ids[0]
  }
}

Use locals in mock attributes

In the following example, the locals block uses conditional expressions to determine resource configurations based on the environment.


locals {
  environment = "production"
  env_prefix  = local.environment
  vpc_name    = "${local.env_prefix}-vpc"
  
  instance_type = local.environment == "production" ? "t3.medium" : "t3.micro"
}

resource "aws_vpc" "main" {
  attrs = {
    cidr_block = "10.0.0.0/16"
    tags = {
      Name        = local.vpc_name
      Environment = local.environment
    }
  }
}

resource "aws_instance" "app" {
  attrs = {
    instance_type = local.instance_type
    ami           = "ami-12345678"
  }
}

Test data for multiple scenarios

In the following example, the locals block defines a map of test scenarios with different configurations that resource test cases reference to test various size requirements.

locals {
  test_scenarios = {
    small = {
      instance_type = "t3.micro"
      volume_size   = 10
    }
    medium = {
      instance_type = "t3.medium"
      volume_size   = 50
    }
    large = {
      instance_type = "t3.large"
      volume_size   = 100
    }
  }
}

resource "aws_instance" "small" {
  attrs = {
    instance_type = local.test_scenarios.small.instance_type
    ami           = "ami-12345678"
  }
}

resource "aws_ebs_volume" "small" {
  attrs = {
    availability_zone = "us-east-1a"
    size              = local.test_scenarios.small.volume_size
  }
}

resource "aws_instance" "large" {
  attrs = {
    instance_type = local.test_scenarios.large.instance_type
    ami           = "ami-12345678"
  }
}