1. What is a test case:
IEEE Standard 610 (1990) defines test case as follows:
"(1) A set of test inputs, execution conditions, and expected results developed for a particular objective, such as to exercise a particular program path or to verify compliance with a specific requirement.
"(2) (IEEE Std 829-1983) Documentation specifying inputs, predicted results, and a set of execution conditions for a test item."
In Simple terms the test case can be defined as below:
A Test Case is set of preconditions and steps to be followed with input data and expected behavior to validate functionality of a system.
In simple words a test case is brief description of what to test and how to test