Net::HTTP.get_response with local files "file://..."


In my application I fetch a webpage with Net::HTTP.get_response(url).
For creating a unit test I don't want to be depended on an internet connection. So I tried to give an url like that: "file:///c:/mydir/mypage.html" (this url works in webbrower). But it seems that this is not the right protocol for Net::HTTP. Is there any possibility to use such "file:///"-urls with Net::HTTP or do I have to check for the protocol and open the file directly?