anchor.diff:  [<Test;Parallelizable>]
   let ``tx monad using`` () = 
       let c = withMemDb()
  -    let tran() = tx {
  +    let tran = tx {
           do! txInsert 3
           use! reader = Tx.execReader "select * from person" []
           let id = 
  
positive.code:         with e ->
              do! txInsert 3
      }
      let result = tran() c
      match result with
      | Tx.Commit a -> Assert.AreEqual(2L, countUsers c)
      | Tx.Rollback a -> failwith "Transaction should not have failed"
      | Tx.Failed e -> failwithe e "Transaction should not have failed"
      
negative.code:             |> Enumerable.First
          return id
      }
      let result = tran c
      match result with
      | Tx.Commit a -> Assert.AreEqual(3, a)
      | Tx.Rollback a -> failwith "Transaction should not have failed"
  