Control Flow Testing

In software engineering, Control Flow Testing is a white-box testing technique that focuses on the execution paths through a program. It uses the program's control structure, which is graphically represented as a Control Flow Graph (CFG), to systematically design test cases.

The goal is to verify the logical correctness of the program by examining its decision points and paths. The CFG is a directed graph where nodes represent basic blocks of code (a sequence of statements with one entry and one exit point), and edges represent the flow of control between these blocks, such as an if condition leading to two different paths.

Key Coverage Criteria Control Flow Testing encompasses several levels of coverage criteria, each with increasing rigor:

• Statement Coverage: This is the most basic form. It aims to design test cases that execute every statement in the source code at least once. It helps in identifying dead code but can miss logical errors in decision points.

• Branch Coverage (Decision Coverage): A stronger criterion that requires every possible outcome (e.g., true and false) of each decision point (like if, while, switch statements) to be tested. It ensures that all branches from a decision node are traversed.

• Path Coverage: This is the most comprehensive and demanding criterion. It aims to test every possible path from the entry point to the exit point of the program's control flow graph. For programs with loops, the number of paths can be infinite, making 100% path coverage impractical.

• Basis Path Testing: A practical approach to path testing developed by Thomas McCabe. It uses the program's cyclomatic complexity to determine the number of linearly independent paths. Testing this basis set of paths guarantees that every statement and branch in the program is executed at least once.

Example Consider the following function:

function getGrade(score) {
  if (score >= 90) {
    return 'A'; // Path 1
  } else {
    return 'B'; // Path 2
  }
}

To achieve 100% branch coverage, two test cases are needed:

1. A test case where score is 90 or greater (e.g., score = 95) to test the true branch.
2. A test case where score is less than 90 (e.g., score = 80) to test the false branch.