How do get the value of a post request?

I'm doing some though testing and I'd like to get the value of what was posted. Here I'm using a simple test of request's post function to demonstrate what I'm attempting to do.

nock('http://example.com').post('/');

request.post('http://example.com', postValue, stubFunction);

process.nextTick() {
  asert( ???? = postValue);
}