When White-Box, Black-Box, and Grey-Box Test Cases Can Be Created: 25-Comp-B11 Advanced Software Design, December 2019, Q6

Question 6 of 28: When White-Box, Black-Box, and Grey-Box Test Cases Can Be Created

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

Notes on this paper

17-Comp-B11 Advanced Software Design — National Exams, December 2019. 3 hours, closed book exam with one aid sheet 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; Pressman, Software Engineering: A Practitioner's Approach (9th ed.) — supplementary process and quality coverage; Gamma, Helm, Johnson & Vlissides (GoF), Design Patterns: Elements of Reusable Object-Oriented Software — creational/structural/behavioural pattern catalogue and the "program to an interface, not an implementation" / "favor object composition over class inheritance" principles; Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, visibility, and multiple inheritance semantics; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/class invariants; Barbara Liskov's 1987 substitutability paper for Question 12; Karl Wiegers, Software Requirements (3rd ed.); Myers, The Art of Software Testing, for Question 6.

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

Question 6: When White-Box, Black-Box, and Grey-Box Test Cases Can Be Created (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.

Black-box testing derives test cases purely from the specified external behaviour (inputs/outputs), with no reference to internal structure — so its test cases can be created as soon as the requirements are finalized, before design or code exists at all. A requirement such as "reject any deposit amount ≤ 0" is directly testable without knowing how the module is implemented.

Grey-box testing combines external behaviour with limited internal knowledge — the module's architecture, key data structures, or algorithm choice, without full source-level detail. Its test cases can be created once the design phase has fixed that architecture (component boundaries, chosen algorithms/data structures), because the tester needs to know enough of the internal structure to target integration seams or algorithm-specific edge cases, but does not yet need the actual source code.

White-box testing requires the actual source code — test cases target specific statements, branches, or paths through the control-flow graph — so it can only be created during or after the implementation phase, once the code that defines those paths actually exists.