1) Test Scenarios: Test scenarios are the high level classification of test requirement grouped depending on the functionality of a module.
2) Test Case: Test cases are the set of valid and invalid executable procedure of a test scenario. A test case with valid functionality is called positive test case and a test case with invalid functionality is called negative test case. A test scenario may have one or more test cases associated to it.
3) Test Script: A test scripts for software testing is a short program written in a programming language used to test some portion of the functionality of a software product system. A composed arrangement of steps that used in writing automated test scripts must be performed automatically can also be known as an automated test scripts.