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25-Comp-B11 Advanced Software Design · Undated paper

Question 6 of 28: Test Cases Derivable From the Design Phase

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

17-Comp-B11 Advanced Software Design — National Exams, May 2019. 3 hours, closed book exam with two aid sheets allowed (written on both sides), no calculator permitted. The paper is organized into five parts, and candidates were instructed to answer any five (5) questions in Part I, any three (3) in Part II, any four (4) in Part III, any two (2) in Part IV, and any five (5) in Part V — only the first questions answered, in each part, as they appear in the answer book are marked. All questions carry equal weight, so the 19 questions actually marked (5+3+4+2+5 of 28) each count for 100/19 ≈ 5.26% of the paper. All 28 questions are answered below for completeness.

Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, design principles, testing, dependability, reuse; Pressman, Software Engineering: A Practitioner's Approach (9th ed.) — supplementary process/metrics/quality coverage; Gamma, Helm, Johnson & Vlissides (GoF), Design Patterns: Elements of Reusable Object-Oriented Software — pattern-language structure, the GoF pattern catalogue, and the "favor object composition over class inheritance" / "program to an interface, not an implementation" principles; Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, visibility, encapsulation, interfaces; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/class invariants; Barbara Liskov's 1987 substitutability paper for Question 12; Stroustrup, The C++ Programming Language, for friend/access-control semantics (Question 25).

Question 12 prints “Liskpv substitution principle”, a typo in the paper; it is answered as the Liskov substitution principle.

PART I — General Principles (answer any 5 of 7)

Question 6: Test Cases Derivable From the Design Phase (Part I)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Design-phase artifacts fix enough detail to derive several classes of test case BEFORE any code exists:

Interface/contract test cases, derived from a class diagram's method signatures together with their design-by-contract preconditions/postconditions (Questions 8–10). Example: once AddressBookManager.add(Contact c) (Question 4) is designed with the precondition "c must not be null and must have a non-empty name," the test case "call add(null), expect the precondition violation to be signalled" can be written immediately.

Structural (white-box) test cases, derived from an algorithm's design-level control-flow (pseudocode or a flowchart) rather than its final source — e.g. a documented loop invariant on a search algorithm already tells a tester which boundary indices (0, last element, empty collection) must be exercised.

State-based test cases, derived from a state-machine/statechart design: one test case per designed state transition, before the state machine is implemented in any particular language.

Integration test cases, derived from a sequence/collaboration diagram showing the order objects are expected to call one another — a test verifying that FileStorage.save() is invoked with the exact list AddressBookManager currently holds can be specified directly from the collaboration design.