BeforeAll {
    $ScriptFile = ".\HammingDifference.ps1"
    $CommandName = "Get-HammingDifference"

    # Remove the function if its already found
    If (Get-Command $CommandName -ErrorAction SilentlyContinue){
        Write-Verbose "Removing the existing $CommandName function from memory as it is already loaded"
        Remove-Item -Path "Function:\$CommandName"
    }

    # Load the script file
    If (Test-Path "$ScriptFile"){
        Write-Output ("Loading: {0}" -f "$ScriptFile")
        . "$ScriptFile"
    }
    Else {
        # Display an error and stop the tests
        Write-Error "The file $ScriptFile was not found. You need to create your answer in a file named $ScriptFile" -ErrorAction Stop
    }
}

Describe "Get-Hamming Test cases" {

    It "Empty strands" {
        Get-HammingDifference '' '' | Should -Be 0
    }
    
    It "Empty strands" {
        Get-HammingDifference 'A' 'A' | Should -Be 0
    }

    It "Long identical strands" {
        Get-HammingDifference "GGACTGA" "GGACTGA" | Should -Be 0
    }

    It "Complete distance in single nucleotide strands" {
        Get-HammingDifference "A" "G" | Should -Be 1
    }

    It "Complete distance in small strands" {
        Get-HammingDifference "AG" "CT" | Should -Be 2
    }

    It "Small distance in small strands" {
        Get-HammingDifference "AT"  "CT" | Should -Be 1
    }

    It "Small distance" {
        Get-HammingDifference "GGACG" "GGTCG" | Should -Be 1
    }

    It "Small distance in long strands" {
        Get-HammingDifference "ACCAGGG" "ACTATGG" | Should -Be 2
    }

    It "Non-unique character in first strand" {
        Get-HammingDifference "AAG" "AAA" | Should -Be 1
    }

    It "Non-unique character in second strand" {
        Get-HammingDifference "AAA" "AAG" | Should -Be 1
    }

    It "Same nucleotides in different positions" {
        Get-HammingDifference "TAG" "GAT" | Should -Be 2
    }

    It "Large distance" {
        Get-HammingDifference "GATACA" "GCATAA" | Should -Be 4
    }

    It "Large distance in off-by-one strand" {
        Get-HammingDifference "GGACGGATTCTG" "AGGACGGATTCT" | Should -Be 9
    }

    It "Disallow first strand longer" {
        { Get-HammingDifference "AATG" "AAA" } | Should -Throw "Left and right strands must be of equal length."
    }

    It "Disallow second strand longer" {
        { Get-HammingDifference "ATA" "AGTG" } | Should -Throw "Left and right strands must be of equal length."
    }
}