Feature request: Utilities for creating events (ALB, APIGateway) for testing

[chriselion]

Use case

In the "Testing your code" section of the documentation, the example uses a dictionary for an event to pass to the handler function, and there's an additional link to the test event json files.

Neither of those are great for testing event handlers in user code though - building a dictionary is tedious and error prone, and the test events aren't distributed with package and would require changing a lot of fields. In either case, it's not possible to run type checking on the events, and it's easy to make a typo in a field name.

Solution/User Experience

Add utility functions for creating event dictionaries. As an example, something like

def build_alb_event(
    *,
    path: str,
    method: str,
    body: BaseModel | dict | None = None,
    query_params: dict[str, str] | None = None,
    headers: Mapping[str, str | bytes | None] | None = None,
) -> dict[str, Any]:
    event: dict[str, Any] = {
        "httpMethod": method,
        "path": path,
        "requestId": "some_request_id",
        "requestContext": {"elb": {"targetGroupArn": ":target:"}},
    }
    if body is not None:
        if isinstance(body, BaseModel):
            event["body"] = body.model_dump_json()
        else:
            event["body"] = json.dumps(body)

    if query_params is not None:
        event["queryStringParameters"] = query_params

    if headers:
        event["headers"] = headers

    return event

(This is missing some things like multiValueQueryStringParameters, but hopefully it gets the idea across)

Alternative solutions

Another approach would be to make new Pydantic models, then you could call `.model_dump()` on the end. The existing event classes that inherit from BaseProxyEvent (e.g. ALBEvent) aren't suitable for this, though.

Acknowledgment

• This feature request meets Powertools for AWS Lambda (Python) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Java, TypeScript, and .NET