let testAdd : unit =
        let output = (vec2d.add (1.0, 1.0) (1.0, 1.0)) = (2.0, 2.0)
        do printfn "add "
        do printfn " output: %A" output

    let testLen : unit =
        let output = (vec2d.len (3.0, 4.0)) = 5.0
        do printfn "len "
        do printfn " output: %A" output

    let testAng : unit =
        let input = (-2.0, 0.0)
        let output = (vec2d.ang input)
        do printfn "ang "
        do printfn "%A" output
        do printfn " output: %b" (output < 3.2 && output > 3.1)

    let scaleTest : unit =
        let output = (vec2d.scale 2.0 (2.0, 3.0)) = (4.0, 6.0)
        do printfn "scale "
        do printfn " output: %A" output

    let dotTest : unit =
        let output = (vec2d.dot (2.0, 5.0) (5.0, 2.0)) = 20.0
        do printfn "dot "
        do printfn " result: %A" output