Check if user exists in SharePoint group using powershell

Hi,

I am adding the users to the SharePoint group as below

$user = $web.Site.RootWeb.EnsureUser($username)

$ownerGroup = $web.SiteGroups["groupname"]

$ownerGroup.AddUser($user)

But i want to test if user is already available in group.

If user is available,want to display the message as user already exists.

But may i not the possibilities of checking if user is available in the SharePoint group.

Please provide your inputs on the same.

Regards,

Sudheer

Thanks & Regards, Sudheer