code: public Response post(String service, Request request, File file) throws IOException {
          if (file != null) {
              this.contentType = MULTIPART + BOUNDARY;
          }
          return call(Method.POST, service, request, file);
      }
docs: A basic http post call
  
  @param service - the endpoint of the service under test
  @param request - the parameters to be passed to the endpoint for the service
  call
  @param file    - a file to upload, accompanied with the post
  @return Response: the response provided from the http call