Receiving Error: Unsupported attribute when trying to create module test for AWS resources

Terraform
1

My team and I have been looking at adding testing to our Terraform codebase. Came across the Module Testing Experiment and have been attempting to create a POC based on what has been documented. Created a dummy module that only defines an s3 bucket.
modules/test_module/main.tf

locals {
  name                  = "test_module"
  description        = "Module used ofr POC of Terraform Tests"
  tags = {
    project   = "test_module"
  }
resource "aws_s3_bucket" "this" {
  bucket = "test-module-bucket"
  acl    = "private"
  tags   = local.tags
  cors_rule {
    allowed_headers = ["*", ]
    allowed_methods = ["POST", ]
    allowed_origins = ["*", ]
    expose_headers  = []
    max_age_seconds = 3000
  }
}

modules/test_module/tests/defauts/test_defaults.tf

terraform {
  required_providers {
    test = {
      source = "terraform.io/builtin/test"
    }
  }
}
provider "aws" {
  region = "us-east-1"
}

module "main" {
  source = "../.."
}

locals{
  bucket = module.main.aws_s3_bucket.this
}
resource "test_assertions" "test_bucket" {
  component = "test_bucket"

  equal "bucket_a_is_private" {
    description = "ensure bucket is private"
    got         = local.bucket.acl
    want        = "private"
  }

  check "environment" {
    description = "default environment is development"
    condition   = can(regex("test-module-bucket", local.bucket.bucket))
  }
}

But whenever I run terraform test in modules/test_module I receive

 Error: Unsupported attribute
│ 
│   on tests/defaults/test_defaults.tf line 17:
│   (source code not available)
│ 
│ This object does not have an attribute named "aws_s3_bucket".

I’m not sure what I’m missing, according to the official docs and the little 3rd party docs covering the testing experiment this test should be executing.

2

That error isn’t related to the testing, but due to an issue with how you are trying to reference things. To refer to variables or resources within a module you need to expose it by adding an output block. so in your case you need to add this to the test_module/main.tf:

output "bucket" {
  value = aws_s3_bucket.this
}

And then reference it as module.main.bucket.

3

Thank you @stuart-c !! Was that, terrible habit we have of not utilizing outputs correctly.