functions/domainlevel/Test-DMDomainLevel.ps1

function Test-DMDomainLevel
{
<#
    .SYNOPSIS
        Tests whether the target domain has at least the desired functional level.
     
    .DESCRIPTION
        Tests whether the target domain has at least the desired functional level.
     
    .PARAMETER Server
        The server / domain to work with.
         
    .PARAMETER Credential
        The credentials to use for this operation.
     
    .EXAMPLE
        PS C:\> Test-DMDomainLevel -Server contoso.com
     
        Tests whether the domain contoso.com has at least the desired functional level.
#>

    [CmdletBinding()]
    param (
        [PSFComputer]
        $Server,
        
        [PSCredential]
        $Credential
    )
    
    begin
    {
        $parameters = $PSBoundParameters | ConvertTo-PSFHashtable -Include Server, Credential
        $parameters['Debug'] = $false
        Assert-ADConnection @parameters -Cmdlet $PSCmdlet
        Invoke-Callback @parameters -Cmdlet $PSCmdlet
        Assert-Configuration -Type DomainLevel -Cmdlet $PSCmdlet
        Set-DMDomainContext @parameters
    }
    process
    {
        $levelValues = @{
            '2008R2' = 4
            '2012'   = 5
            '2012R2' = 6
            '2016'   = 7
        }
        $level = Get-DMDomainLevel
        $desiredLevel = $levelValues[$level.Level]
        $tempConfiguration = $level | ConvertTo-PSFHashtable
        $tempConfiguration['DesiredLevel'] = [Microsoft.ActiveDirectory.Management.ADDomainMode]$desiredLevel
        $domain = Get-ADDomain @parameters
        if ($domain.DomainMode -lt $desiredLevel)
        {
            New-TestResult -ObjectType DomainLevel -Type Raise -Identity $domain -Server $Server -Configuration ([pscustomobject]$tempConfiguration) -ADObject $domain
        }
    }
}