anchor.diff:                  2 -- 4
                   3 -- 4
               }"
  -            let g = load_undirected_test_graph
  -            let v = Visualisation.toDotGraphDescriptionLanguage g
  -            checkDotLanguage v expected            
  +            trial {
  +                let! g = load_undirected_test_graph
  +                return Visualisation.toDotGraphDescriptionLanguage g
  +            }
  +            |> returnOrFail |> checkDotLanguage expected
   
           testCase "directed graph" <| fun _ ->
               let expected = "digraph {
  
positive.code:               a * (b + c) = a * b + a * c
  
      ]
  //////////////////////////////////////////////////////////////////////////////////////////////////////////////
      
  [<EntryPoint>]
  let main args =
  
negative.code:                             for ks in choose (j+1) (i-1) do
                              yield n.[j] :: ks ]
              in choose 0 k  
  
      let expectOneFailedWith f result = 
          result |> failed |> should be True
          match result with 
          | Bad [e] -> f e
          | _ -> false        
  
      let isParsingFailure (gf: GraphFailure) = 
          match gf with 
          | ParsingFailure(_) -> true
          | _ -> false
                        
   
  open TestUtils
  