How can I create a lambda event template via terraform?

I did try something and it worked. I must warn that this is reverse engineering and may break anytime in future, but works well for me so far.

As per Amazon doc for testing lambda functions, whenever a Shareable Test Event is created for any lambda, it is stored under a new schema under the lambda-testevent-schemas schema registry.

I made use of this information and figured out the conventions AWS follows to keep track of the events so that I can use those to manage resources using terraform

1. The name of the schema is _<name_of_lambda_function>-schema, hence, from terraform I manage a new schema named _<name_of_lambda_function>-schema

resource "aws_schemas_schema" "my_lambda_shared_events" {
  name          = "_${aws_lambda_function.my_lambda.function_name}-schema"
  registry_name = "lambda-testevent-schemas"
  type          = "OpenApi3"
  description   = "The schema definition for shared test events"
  content       = local.my_lambda_shared_events_schema
}

2. I create a json doc (my_lambda_shared_events_schema) which follows the OpenAPI3 convention. For example =>

{
  "components": {
    "examples": {
      "name_of_the_event_1": {
        "value": {
          ... the value you need ...
        }
      },
      "name_of_the_event_2": {
        "value": {
          ... the value you need ...
        }
      }
    },
    "schemas": {
      "Event": {
        "properties": {
          ... structure of the event you need ...
        },
        "required": [... any required params ...],
        "type": "object"
      }
    }
  },
  "info": {
    "title": "Event",
    "version": "1.0.0"
  },
  "openapi": "3.0.0",
  "paths": {}
}

After terraform apply, you should be able to see the terraform managed shareable events in AWS console.

Some important gotchas when using this method:

1. If you add events using terraform using this method, any events added from the console would be lost.
2. The schema registry lambda-testevent-schemas is a special registry & must NOT be managed using terraform as it may disrupt other lambda functions' events created outside the scope of this terraform module.
3. It is required for the lambda-testevent-schemas to be available beforehand. You can either have a check to create this registry before the module is applied or else create any random shareable event for any random lambda function. This needs to be done once per region per account.
4. If you face difficulties creating the json schema for your lambda, you can for once create the events from console and then copy the json from EventBridge schema registry.