PrimeFactorsFsharp

PrimeFactors.fs

namespace PrimeFactors

module PrimeFactors = 
    type IPrimeChecker =
        abstract member IsPrime : int64 -> int64 -> bool        

    type PrimeFactors() = 
        interface IPrimeChecker with
            member this.IsPrime number i =
                number % i = 0L

        member this.CheckPrimes number i acc =
            if i > (number |> float |> sqrt |> int64) then
                number::acc
            elif (this :> IPrimeChecker).IsPrime number i then
                this.CheckPrimes (number / i) i (i::acc)
            else
                this.CheckPrimes number (i + 1L) acc

        member this.Of number =
            if number = 1L then
                [||]
            else
                this.CheckPrimes number 2L [] |> List.toArray

PrimeFactorsMock.fs

namespace PrimeFactors
open PrimeFactors

module PrimeFactorsMock =
    type PrimeFactorsMock() =
        inherit PrimeFactors() 

        let mutable stepCount = 0L

        interface IPrimeChecker with
          member this.IsPrime number i =
            stepCount <- stepCount + 1L
            number % i = 0L

        member this.StepCount number =
            stepCount <- 0L
            this.Of number |> ignore
            stepCount

PrimeFactorTests.fs

namespace PrimeFactors

open PrimeFactors
open NUnit.Framework
open FsUnit
open PrimeFactorsMock

[<TestFixture>]
module PrimeFactorTests =

    [<TestCase(1L, [||])>]
    [<TestCase(2L, [|2L|])>]
    [<TestCase(3L, [|3L|])>]
    [<TestCase(4L, [|2L; 2L|])>]
    [<TestCase(6L, [|3L; 2L|])>]
    [<TestCase(8L, [|2L; 2L; 2L|])>]
    [<TestCase(16L, [|2L; 2L; 2L; 2L|])>]
    [<TestCase(773L, [|773L|])>]
    let prime_factors_of_number number expect =
        PrimeFactors().Of number |> should equal expect

    [<TestCase(1L, 0L)>]
    [<TestCase(4L, 1L)>]
    [<TestCase(773L, 26L)>]
    let step_count_of_number number stepCount =
        PrimeFactorsMock().StepCount number |> should equal stepCount