Is there ANY good HTTP mocking package for node?

I'm very new to Node.js, so I might just not be getting it, but after searching quite a bit, and trying a few different solutions, I am still not able to find a decent way to mock API responses using Node for acceptance testing.

I've got a javascript app (written in elm actually) that interacts with an API (pretty common, I imagine), and I want to write some acceptance tests... so I setup WebdriverIO with selenium and mocha, write some tests, and of course now I need to mock some API responses so that I can setup some theoretical scenarios to test under.

mock-api-server: Looked pretty nice, but there's no way to adjust the headers getting sent back from the server!

mock-http-server: Also looked pretty nice, lets me adjust headers, but there's no way to reset the mock responses without shutting down the whole server... !? And that has issues because the server won't shut down while the browser window is still open, so that means I have to close and relauch the browser just to clear the mocks!

json-server: Simple and decent way to mock some responses, but it relies entirely on files on disk for the responses. I want something I can configure from within a test run without reading and writing files to disk.

Am I missing something? Is this not how people do acceptance testing in the Node universe? Does everyone just use a fixed set of mock data for their entire test suite? That just sounds insane to me... Particularly since it seems like it wouldn't be that hard to write a good one based on express server that has all the necessary features... does it exist?

Necessary Features:

1. Server can be configured and launched from javascript
2. Responses(including headers) can be configured on the fly
3. Responses can also be reset easily on the fly, without shutting down the server.