A use case is a description of how a user interacts with a system to achieve a goal or perform a task. A use case typically consists of a sequence of steps or actions that the user and the system perform to complete the goal or task. A use case can be used as a basis for designing test cases that verify the functionality and usability of the system under test. A test sequence that represents a possible use case should follow the logical order and flow of the user-system interaction and cover the main scenario and possible variations or exceptions. For example, based on the test cases given for a Library Management System, we can identify the following use cases:

UC1: Add a new borrower to the system

UC2: Update a borrower’s data

UC3: Remove a borrower from the system

UC4: Loan a book to a borrower

UC5: Return a book from a borrower

UC6: Reserve a book for a borrower

UC7: Send “reservation ready” message to a borrower

The test sequence that represents a possible use case is D. 1-2-6-7-4-5-3. This test sequence follows the logical order and flow of the user-system interaction and covers the main scenario and possible variations or exceptions. For example:

TC1: Add a new borrower to the system -> This is the first step of the use case, where the user registers as a new borrower in the system.

TC2: Update a borrower’s data -> This is a possible variation of the use case, where the user updates their personal or contact information in the system.

TC6: Reserve a book for a borrower -> This is the second step of the use case, where the user reserves a book that they want to borrow from the library.

TC7: Send “reservation ready” message to a borrower -> This is the third step of the use case, where the system sends a message to the user informing them that their reserved book is ready for pickup.

TC4: Loan a book to a borrower -> This is the fourth step of the use case, where the user picks up their reserved book from the library and loans it from the system.

TC5: Return a book from a borrower -> This is the fifth step of the use case, where the user returns their borrowed book to the library and returns it to the system.

TC3: Remove a borrower from the system -> This is a possible exception of the use case, where

the user decides to cancel their membership and remove their account from the system.

The other test sequences do not represent possible use cases because they do not follow the logical order and flow of the user-system interaction or they do not cover the main scenario and possible variations or exceptions. For example:

A. 1-4-2-7-5-6-3 -> This test sequence does not follow the logical order and flow of the user-system interaction because it performs some steps before or after they are supposed to happen. For example, it performs TC4 (Loan a book to a borrower) before TC6 (Reserve a book for a borrower), which does not make sense because the user cannot loan a book that they have not reserved yet.

B. 1-6-2-5-7-4-3 -> This test sequence does not follow the logical order and flow of the user-system interaction because it performs some steps before or after they are supposed to happen. For example, it performs TC5 (Return a book from a borrower) before TC4 (Loan a book to a borrower), which does not make sense because the user cannot return a book that they have not loaned yet.

C. 1-6-4-7-5-3-2 -> This test sequence does not cover the main scenario and possible variations or exceptions because it omits some steps that are essential for completing or terminating the use case. For example, it omits TC2 (Update a borrower’s data), which is a possible variation of the use case that allows the user to change their personal or contact information in the system.

You can find more information about use cases and test sequences in [A Study Guide to the ISTQB® Foundation Level 2018 Syllabus], Chapter 4, Section 4.2.