private/Tests/Test-MDTInstallDir.ps1

function Test-MDTInstallDir {
    <#
    .SYNOPSIS
        Returns $true when the MDT installation directory exists on disk.
 
    .DESCRIPTION
        Reads the 'Install Dir' value from HKLM:\SOFTWARE\Microsoft\Deployment 4
        and tests whether the directory exists. Falls back to the default MDT
        install location when the registry key is absent.
 
        Returns $false when neither the registry path nor the default directory
        exists on disk.
 
    .NOTES
        Author: David Segura
        Company: Recast Software
        Registry key: HKLM:\SOFTWARE\Microsoft\Deployment 4
        Registry value: Install Dir
        Default path: C:\Program Files\Microsoft Deployment Toolkit
 
    Dependencies:
      Windows Features: MDT
    #>

    [OutputType([bool])]
    param ()

    $installDir = (Get-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\Deployment 4' -Name 'Install Dir' -ErrorAction SilentlyContinue).'Install Dir'

    if ($installDir -and (Test-Path -Path $installDir)) {
        return $true
    }

    # Fallback to default location (registry key absent but directory may exist)
    $defaultPath = Join-Path $env:ProgramFiles 'Microsoft Deployment Toolkit'
    return (Test-Path -Path $defaultPath)
}