Updates tests for content length headers
Updates tests for content length headers

This is just modifying the tests created by @simi, with a couple of
(arguably) improvements.

  * DAMP not DRY.
  * Avoid a few Mistery guests.

Jesus/dropbox_api_v2,Jesus/dropbox_api,Jesus/dropbox_api_v2,Jesus/dropbox_api,Jesus/dropbox_api