Install or upgrade Pester (including PowerShell 2.0 on Windows 7 and Server 2008 r2)

InstallOrUpgradePester.ps1

Write-Output "=== Checking if Pester module is installed ==="
if ( (get-module -ListAvailable pester).count -gt 0 ) {
    write-Output "`tPester is installed. Checking version(s)..."
    if ( (get-module -ListAvailable pester | where-object { $_.version.Major -ge 4} ).count -eq 0 ) {
        write-Output "`tReinstalling latest version of Pester"
        $module = "C:\Program Files\WindowsPowerShell\Modules\Pester"
        takeown /F $module /A /R
        icacls $module /reset
        icacls $module /grant "*S-1-5-32-544:F" /inheritance:d /T
        Remove-Item -Path $module -Recurse -Force -Confirm:$false

        Install-PackageProvider -Name NuGet -MinimumVersion 2.8.5.201 -Force
        Install-Module -Name Pester -Force
    }
} else {
    write-Output "`tPester is not installed. Installing..."
    if( $psversiontable.psversion -ge [version]'5.0') {
        Install-PackageProvider -Name NuGet -MinimumVersion 2.8.5.201 -Force
        Install-Module -Name Pester -Force
    }else{
        # Set to use TLS1.2
        $p = [Enum]::ToObject([System.Net.SecurityProtocolType], 3072);
        [System.Net.ServicePointManager]::SecurityProtocol = $p;

        # Download PsGet module (to get Install-Module functionality in PowerShell 2.0)
        $tempPath = 'C:\source\temp\psget'
        New-Item $tempPath -ItemType Directory -Force | Out-Null
        $client = (New-Object Net.WebClient)
        $client.DownloadFile('https://raw.githubusercontent.com/psget/psget/master/PsGet/PsGet.psm1', "$tempPath\PsGet.psm1")

        Import-Module "$tempPath\PsGet.psm1"
        Install-Module -Module Pester
    }
}