Develop an AWS CloudFormation template that includes a transit gateway attachment and associated routing configurations. Use this template to create a CloudFormation stack set, deploying a new stack for each VPC in the account, and set up a new VPC for each test environment.

Establish a single VPC for all test environments, incorporating a transit gateway attachment and associated routing configurations. Utilize AWS CloudFormation to deploy all test environments into this VPC.

Create a new organizational unit (OU) in AWS Organizations dedicated to testing. Design an AWS CloudFormation template that encompasses a VPC, essential networking resources, a transit gateway attachment, and associated routing configurations. Use this template to create a CloudFormation stack set for deployment into each account under the testing OU, and establish a new account for each test environment.

Transform the test environment EC2 instances into Docker images. Employ AWS CloudFormation to set up an Amazon Elastic Kubernetes Service (Amazon EKS) cluster in a new VPC, create a transit gateway attachment, and establish associated routing configurations. Leverage Kubernetes to manage the deployment and lifecycle of the test environments.