test "Increment":
func increment(x: var int)
{.Post: [x > `x@old`],
Pre : [x < int.high].} =
x = x + 1

func increment(x: int; cnt: int = 1): int
{.Pre : [x < int.high],
Post: [result > x].} =
x + cnt

var x: int = 1
increment x
assert x == 2

let y: int = increment(6)
assert y == 7