As I discussed previously I believe that to follow good practice I try to ensure that database permissions are granted by role membership and each role is created with the minimum amount of permissions required for successful execution of the task involved.
So with each database having the correct roles created and the users created we just need to add the user to the database and to the role. This is easily done with PowerShell.
The Add-UserToRole function takes four parameters Server,Database,User and Role and does a series of error checks.
With these functions you can easily create a number of Users and add them to database roles quickly and easily and repeatedly.
If the test team come to you and require 10 Test Users and 3 Test Administrators adding to the test database. I create 2 notepad files
and use them with the Add-SQLAccountToSQLRole and Add-UserToRole functions to create the users
Here are the results in PowerShell
and in SSMS
The Code is here Add-UserToRole