anchor.diff:  
   [<Fact>]
   let ``POST "/either" with unsupported Accept header returns 404 "Not found"`` () =
  +    let app = 
  +        choose [
  +            GET >>= choose [ 
  +                route "/"     >>= text "Hello World"
  +                route "/foo"  >>= text "bar" ]
  +            POST >>= choose [
  +                route "/text"   >>= mustAccept [ "text/plain" ] >>= text "text"
  +                route "/json"   >>= mustAccept [ "application/json" ] >>= json "json"
  +                route "/either" >>= mustAccept [ "text/plain"; "application/json" ] >>= text "either" ]
  +            setStatusCode 404 >>= text "Not found" ]
  +
       let headers = new HeaderDictionary()
       headers.Add("Accept", new StringValues("application/xml"))
       ctx.Request.Method.ReturnsForAnyArgs "POST" |> ignore
  
positive.code: 
  [<Fact>]
  let ``POST "/json" with supported Accept header returns "json"`` () =
      let headers = new HeaderDictionary()
      headers.Add("Accept", new StringValues("application/json"))
      ctx.Request.Method.ReturnsForAnyArgs "POST" |> ignore
  
negative.code: 
      let result = 
          { HttpContext = ctx; Services = services }
          |> app
          |> Async.RunSynchronously
  
      match result with
      | None     -> assertFailf "Result was expected to be %s" expected
      | Some ctx ->
          let body = getBody ctx
          Assert.Equal(expected, body)
  
  [<Fact>]
  let ``GET "/foo/blah blah/bar" returns "blah blah"`` () =
      let app =
          GET >>= choose [ 
              route   "/"       >>= text "Hello World"
              route   "/foo"    >>= text "bar"
              routef "/foo/%s/bar" text
              routef "/foo/%s/%i" (fun (name, age) -> text (sprintf "Name: %s, Age: %d" name age))
              setStatusCode 404 >>= text "Not found" ]
  
      ctx.Request.Method.ReturnsForAnyArgs "GET" |> ignore
      ctx.Request.Path.ReturnsForAnyArgs (PathString("/foo/blah blah/bar")) |> ignore
      ctx.Response.Body <- new MemoryStream()
  