anchor.diff:  let ``find non-existent record``() =
       withDatabase (fun conn ->
           findNonExistentRecord (Sql.withConnection conn))
  +
  +[<Test>]
  +let ``find non-existent record persistent``() =
  +    findNonExistentRecord (withNewDbFile())
   
   let findExistentRecord conn = 
       insertUser conn {id = 1; name = "pepe"; address = None}
  
positive.code: 
  [<Test>]
  let ``insert then get persistent`` () = 
      insertThenGet (recreateDbFile())
  
  let findNonExistentRecord conn = 
      let p = findUser conn 39393
  
negative.code:         conn
      withResource createConnectionAndSchema (fun c -> c.Dispose()) f
  
  let withNewDbFile() =
      File.Delete "test.db"
      createSchema (createPersistentConnection())
      Sql.withNewConnection createPersistentConnection
  