When testing deployments of Azure RM resources (ie. using the Test-AzureRmResourceGroupDeployment powershell cmdlet) an empty Resource Group is created.
This Resource Group is often not needed at this point and can be deleted after you are done testing the deployment of the resources.
For deleting the Resource Group you can use the VSTS task delete resource group if empty.
This tasks deletes the Resource Group only if it does not contains any resources.