AddTestableFunction

namespace Bad
open System;

module BadDependency =
    let BadFunction x = 
        Random().Next(0, x)

module TestMe =
    let FuncToTest y =
        (y + BadDependency.BadFunction 100) % 2 = 0

module Test =
    let Test () =
        // Can't replace call to BadFunction
        let result = TestMe.FuncToTest 42
        0

///////////////////////////////////
// Refactor to this
///////////////////////////////////
namespace Better
open System;

module BadDependency =
    let BadFunction x = 
        System.Random().Next(0, x)

module TestMe =

    let TestableFuncToTest f y =
        (y + f 100) % 2 = 0

    [<Obsolete("Use TestableFuncToTest")>]
    let FuncToTest y = TestableFuncToTest BadDependency.BadFunction


module Test =
    let Test () =
        let mock x = 2
        let result = TestMe.TestableFuncToTest mock 42
        // Assert is now possible
        0