VM with DynamicParam.ps1

Function Test-VM {
    [cmdletBinding()]
    Param(
        [Parameter]
        [string]
        $dummy
    )
    #Dynamic Params require [CmdletBinding()], but are defined on their own outside the main Param() block
    DynamicParam {
        $ParameterName = 'VM'

        $RuntimeDict = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary
        $Attribs = New-Object System.Collections.ObjectModel.Collection[System.Attribute]

        $ParameterAttributes = New-Object System.Management.Automation.ParameterAttribute
        $ParameterAttributes.Mandatory = $true
        $ParameterAttributes.Position = 0

        $Attribs.Add($ParameterAttributes)

        $Dataset = Get-VM | Select-Object -ExpandProperty Name
        $ValidateSet = New-Object System.Management.Automation.ValidateSetAttribute($Dataset)

        $Attribs.Add($ValidateSet)

        $RuntimeParam = New-Object System.Management.Automation.RuntimeDefinedParameter($ParameterName, [string[]], $Attribs)
        $RuntimeDict.Add($ParameterName, $RuntimeParam)
    
        return $RuntimeDict
    }

    #Pull out the Dynamic Param from BoundParameters so you can use it
    Begin {$VM = $PSBoundParameters[$ParameterName]}

    Process {
        #Do stuff with that VM, here.
        Write-Output "You selected: $VM"
    }

    End {}

}