In a professional edition environment we haven't access to the sandboxes. So we can't have test sandbox for the end users. Is there any alternatives to have two different environments both accessible to the end users? (A production environment and a test one)
You could use https://developer.salesforce.com/ to develop things for free.
https://developer.salesforce.com/page/An_Introduction_to_Environments has some more information, including number of user licences etc.