Pre-Condition is the condition which needs to be fulfilled before executing the test case
Post Condition is the State which we will get if we execute the steps successfully .
Lets take an example :- You want to Invite a friend to Join to Social Media
Pre-condition :- You need to have an account and need to Login before you proceed .
Test Case --> Login to QT ---> Home page opens ---> Click on Invite ---> Invite Your Contact page opens --> Click on "Enter Email Addresses Manually "---> Enter the email address in "Send to " Field ---> Enter Your Message --> Click on Send Invitations.
Post Condition ---> Invitation mail sent to the Corresponding Email address ..