TEST CASE –
A test case is a set of conditions and steps that when followed/applied, a tester can determine whether a feature, an application or a software system is working as originally designed.
A test case usually contains References to the original task, Pre-conditions ( if the pre-conditions are not met, testing can not continue), Steps (steps describe what a tester needs to do in order to get a result), Expected Result (what should happen after following all the described steps) but may also contain Estimation, Priority, Environment on which to perform test.
Example of a test case :-
Title – Perform a login action on mail.google.com with an invalid password
Test steps :
Expected Result – A error message will be displayed under the Password field with red letters stating "Wrong password. Try again"