ParameterSet3.ps1

Function MyFunction
{
    [cmdletbinding(DefaultParameterSetName="ProcessSet")]
    
    param([parameter(Mandatory,ParameterSetName="ServiceSet")]$service,
          [parameter(Mandatory,ParameterSetName="ProcessSet")]$Process,
          $Test)

          switch($PSCmdlet.ParameterSetName)
          {
              "ServiceSet" {Write-host "Service: $service" -ForegroundColor Green}
              "ProcessSet" {Write-host "Process: $process" -ForegroundColor Yellow}

          }

          if($test)
          {
            Write-host "test: $test" -ForegroundColor Magenta
          }
}

write-host "about to call with NO PARAMS" -ForegroundColor Cyan
MyFunction