Licensing is a complex matter and it's easy to get things wrong.
That said, as far as I know, if you have a MSDN subscription you should be entitled to a test license for each production license. This allows you to test with the exact same edition you will use in production.
The easiest solution is Developer Edition, that costs around $60. You will need a license for each developer using the instance.
Another option is the Enterprise Evaluation Edition, that lets you test the product for 180 days.