List of random numbers with a given sum

ArrayWith.swift

func arrayWith(count: Int, sum : Int) -> [Int] {
    assert(count >= 1)
    var result = [sum]
    while result.count < count {
        let randomIndex = result.indices.randomElement()!
        let v = Int.random(in: 0...result[randomIndex])
        result[randomIndex] -= v
        result.append(v)
    }
    return result
}

final class SumTests: XCTestCase {
    
    func testExample() {
        for i in 1...10 {
            let sum = Int.random(in: 1...1000)
            let count = Int.random(in: 1...1000)
            let array = arrayWith(count: count, sum: sum)
            XCTAssertEqual(count, array.count)
            XCTAssertEqual(sum, array.reduce(0, +))
        }
    }

}