Explain to business stakeholders how to define testable acceptance criteria ?

Each user story comes up with an acceptance criteria e.g say a user story say

As a getskills website user
I should be able to sign up as a student   
So that I can later log  in   and attend  classes

The above user story can have the following acceptance criteria
1. User can sign up with valid email ID
2. User gets a valid notification on sign up
3. User gets a confirmation message during the sign up
4. User should see the sign up confirmation message within a few seconds

Above example covers the functional, security and performance aspects of a user story .The most important thing is that business stakeholders should understand all aspects of a user story. Sometimes you will to have to work with nontechnical product owners and will experience that they are just focused on the functionality, by explaining the impact of security and performance you can help them in defining acceptance criteria
In one of the project I worked the acceptance criteria was as following

-Screen has been developed as per the mock ups
-Automated tests are written and passed
-Business rules and validation have been tested

In another project the acceptance criteria were as following

User can login successfully
Exception handling for the login feature has been      implemented
Feature is secure 
The performance of the Login feature is acceptable