anchor.diff:  
       let ctx = Substitute.For<HttpContext>()
       mockXml ctx
  +    mockJson ctx (Newtonsoft None)
       mockNegotiation ctx config.NegotiationConfig
       let app =
           GET >=> choose [
  
positive.code: 
      let ctx = Substitute.For<HttpContext>()
      mockXml ctx
      mockNegotiation ctx config.NegotiationConfig
      let app =
          GET >=> choose [
  
negative.code:     }
  
  [<Theory>]
  [<MemberData("XmlJsonReturningAcceptHeaderCases")>]
  let ``Get "/auto" with Accept header of "application/json; q=0.5, application/xml" returns XML object`` (config : NegotiationConfigWithExpectedResult) =
      let johnDoe =
          {
  