returning a rejected promise from lambda fails under child process mode

[leemhenson]

Bug Report

Operating under:

serverless-offline:
    useChildProcesses: true

when I have a handler function like so:

export const handler = () => Promise.reject("FOO");

when I send a request I see:

FOOOO
FOOOO
(node:68792) UnhandledPromiseRejectionWarning: FOOOO
(Use `node --trace-warnings ...` to show where the warning was created)
(node:68792) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:68792) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

and no response is returned to the client. I have to kill serverless-offline and restart it.

Expected behavior/code

Under:

serverless-offline:
    useChildProcesses: false

I get a 500 response. I expected the child process version to behave the same.

Environment

• serverless version: 1.71.3
• serverless-offline version: 6.1.7
• node.js version: 13.14.0
• OS: macOS 10.15.3

Additional context/Screenshots

The handler gets invoked here:

https://github.com/dherault/serverless-offline/blob/master/src/lambda/handler-runner/child-process-runner/ChildProcessRunner.js#L52

but when I added additional logging inside the catch block here:

https://github.com/dherault/serverless-offline/blob/master/src/lambda/handler-runner/child-process-runner/ChildProcessRunner.js#L55

I could see it was never getting hit. I also attached childProcess listeners for close, disconnect, error and exit but none are invoked until I kill serverless offline. error is never invoked.

[MorelSerge]

Same here, and I'm using useChildProcesses because of this issue:
#931