application.rb

module Whatsnext
  class Application < Sinatra::Base
    post '/features/*' do
      puts request.body.read
    end
  end
end

env.rb

# RSpec
require 'spec/expectations'

# Webrat
require 'rack/test'
require 'webrat/sinatra'
Webrat.configure do |config|
  config.mode = :sinatra
end

World(Webrat::Matchers, Webrat::HaveTagMatcher, Rack::Test::Methods) do
  context = OpenStruct.new(:app => Whatsnext::Application)
  Webrat::SinatraSession.new(context)
end

steps.rb

When /^I save it as an existing file$/ do
  post("/foo", 'bar')
end