Manual : UseCase VsTest Scenario Vs Test Case

Manual : Test Scenario Vs Test Case

Lets consider a library management system:

Usecase:

The functions performed by different entities(Customer, Staff, Manager) is mentioned in Usecase. a) Staff enters customer information.

Test Scenario:

Test cases are written based on scenario. Test scenarios are very brief.
a)Staff enters customer information
b)Customer returns a book

Test Cases:

Test cases are derived from scenarios. They are step by step instructions. They are very detailed and also contains actual results and expected results along with other fields
a. Enter customer information(Name, address, ph no)
b. Click on save.

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For Example:If i want to validate the login page

Test Scenario will be: User receives an error message when he enters invalid 
                                     parameters in the login page.

Test Cases 1: User receives an error message when he enters valid userid and  
                       invalid password.
Test Cases 2: User receives an error message when he enters invalid userid and
                       valid password
Test Cases 3: User receives an error message when he enters invalid userid and
                       invalid password

Based on the Test Scenario ,Test engineer are writing test cases.

Test Scenario are derived from the Client Requirements.