anchor.diff:  let _ = DateTime.Now
   """
       |> forLine 3
  +    |> andEntity "System.DateTime"
       |> ns "TopLevel"
       |> position """
   module TopLevel
  
positive.code:     let _ = DateTime.Now
  """
      |> forLine 5
      |> ns "TopLevel.Nested"
      |> position """
  module TopLevel
  
negative.code: let file = "C:\\file.fs"
  let languageService = LanguageService(fun _ -> ())
  
  type Line = int
  type Source = string
  type FullEntityName = string
  
  let forLine (line: Line) (source: Source) = source, line
  
  let andEntity (entity: FullEntityName) (source, line) =
      let parseResult =
          languageService.ParseFileInProject(LanguageServiceTestHelper.projectOptions file, file, source) 
          |> Async.RunSynchronously
      if parseResult.ParseHadErrors then failwithf "Cannot parse input: %s, errors: %A" source parseResult.Errors
  