White-Box Testing Strategies: Comprehensive Guide Overview of White-Box Testing White-box testing, also known as clear or glass box testing, is a method of testing software that focuses on the internal structures or workings of an application. The main aim is to validate the inner logic and working of the code, ensuring that the flow of inputs to outputs is as expected. Key Concepts Control Flow Graph (CFG) ● Definition: Describes the sequence in which different instructions of a program are executed. ● Components: Nodes represent program statements; edges represent control flow between statements. ● Drawing CFG: ● Sequence constructs: Simple linear flow from one statement to another. ● Selection constructs: Branches representing conditional statements (e.g., if-else). ● Iterationconstructs: Loops, where control returns to the start of the loop after execution. Path and Linearly Independent Path ● Path: A sequence of nodes and edges from the start to the end of the CFG. ● Linearly Independent Path: A path introducing at least one new edge not included in any other path; provides unique coverage in testing. Cyclomatic Complexity ● Definition: A metric to determine the number of linearly independent paths through a program's source code. ● Computation Methods: ● Method 1: ● Cyclomatic Complexity V(G) = E – N + 2 ● ( E ): Number of edges in CFG ● ( N ): Number of nodes in CFG ● Method 2: Count of bounded areas + 1 in CFG ● Method 3: Number of decision points + 1 Testing Strategies ● Statement Coverage: ● Ensures every statement in the code is executed at least once. ● Example: For Euclid’s GCD algorithm, test cases should ensure all lines are covered. ● Branch Coverage: ● Ensures each outcome (true/false) of each decision point is executed. ● Stronger than statement coverage. ● Condition Coverage: ● Tests all individual boolean sub-expressions within conditions. ● Requires each component of composite conditions to be tested for true and false. ● Path Coverage: ● Involves testing all linearly independent paths through the program. Practical coverage limits testing to just these paths due to possible path explosion in large programs. ● Data Flow Testing: ● Focuses on points where variables receive values and where they are used. ● Definitions (DEF) and Uses (USES) of variables drive the creation of test cases. ● Mutation Testing: ● Introduces small changes (mutants) to the program to check if existing test cases can detect the error. ● Computationally expensive but effective in increasing test robustness. Detailed Examples Euclid’s GCD Algorithm ● Statement Coverage: int compute_gcd(int x, int y) { while (x != y) { if (x > y) x = x - y; else y = y - x; } return x; } ● Test cases: {(x=3, y=3), (x=4, y=3), (x=3, y=4)} ● Branch Coverage: Ensuring true and false branches: Test cases: {(x=3, y=3), (x=3, y=2), (x=4, y=3), (x=3, y=4)} Control Flow Graph Example ● For the sequence construct a=5; b=a*2-1; ● Node: Each assignment. ● Edge: Flow from a=5;to b=a*2-1; ● For the selection construct: if (a > b) c = 3; else c = 5; c = c * c; ● Nodes: Conditional check and assignments. ● Edges: Branching on the condition, converging back to the main flow. Cyclomatic Complexity Calculation ● For given CFG with edges (E) = 7, nodes (N) = 6: ● Using Method 1: V(G) = 7 - 6 + 2 = 3 ● Using Method 2: 2 bounded areas + 1 = 3 Summary White-box testing strategies play a crucial role in ensuring that software's internal logic is correct and that all the paths, branches, and conditions are properly tested. By considering different methods such as statement, branch, condition, path, data flow, and mutation testing, comprehensive coverage and validation of software can be achieved, leading to higher reliability and robustness of the code. By employing tools and systematic methods like CFG and Cyclomatic Complexity, testers can effectively identify the necessary paths and conditions needing verification, thus enhancing the quality of their testing process. For detailed instructions and visual aids on drawing CFGs and computing cyclomatic complexity, refer to the provided examples of sequence, selection, and iteration constructs, and the Euclid’s GCD computation algorithm.