I am trying to create a new web application using PowerShell. I keep getting the error application pool account is not found! How do I solve this? 

I tried adding the new web application to DefaultAppPool as follows:

    New-SPWebApplication -Name "Test WebApp" -ApplicationPool "DefaultAppPool" -ApplicationPoolAccount (Get-SPManagedAccount "WIN2K8R2SPTEST\Administrator") 

But the Cmdlet Get-SPManagedAccount seems to return an empty string. I also tried to change the `ApplicationPool` to SharePoint 80. 

I am running SharePoint Foundation 2010 on a standalone installation. How can I fix this error?