The process of developing a new T-Engine is described on the Creating a T-Engine page. It walks through the steps involved in creating a simple Hello World transformer and includes commands to help test.
When developing new Local Transformers it is generally a good idea to increase the frequency of the polling of the various locations that contain custom Pipeline, Rendition, Mimetype Definitions and also of the Transform Service.
mimetype.config.cronExpression=0 0/1 * * * ? rendition.config.cronExpression=2 0/1 * * * ? local.transform.service.cronExpression=4 0/1 * * * ? transform.service.cronExpression=6 0/1 * * * ?