Control Flow Testing

White Box Testing method that focuses on testing code paths identified by its Control Flow Graph (CFG) by choosing inputs that exercise different code paths.

Control Flow Graph (CFG)

def process_data(data):
    total = 0
    print("total = 0")
    for item in data:
        if item % 2 == 0:
            total += item
        else:
            total += 1
    if total == 0:
        print("Empty")
    else:
        print("Present")
    return total

Directed Acyclic Graph that represents the Python code:

• Process Block contains a group of sequential statements.
• Decision Point represented by diamond. Can be binary (2-case) or n-nary (n-case).

Common Programming Constructs CFG

If statement:

If/Else Statement:

While/For Loop:

Switch Statement:

Test Coverage

Test Coverage Levels:

Level	Coverage	Description
Level 1	100% statement coverage	Every line of code is tested
Level 2	100% branch coverage	Every decision point branch is taken
Level 3	100% basis path coverage	Every linearly independent path is tested
Level 4	100% path coverage	Every path is tested

Total No. of Paths

Total No. of Paths $P$ tested in Level 4: 100% path coverage testing:

• $D$ is no. of binary decision points.
• $L$ is no. of loop iterations

$$P = 2^D \times L$$

Basis Path Testing

Control Flow Testing that focuses on Level 3 Test Coverage: Testing all basis paths aka linearly independent paths in the Control Flow Graph (CFG).

Non Unique Set of basis paths is not unique, depends on initial baseline path chosen.

1. Build CFG from code of System Under Test.

2. Compute Cyclometric Complexity (CC) to determine no. of basis paths to test.

   Not all basis paths identified by CC are feasible (reachable) in code. Such basis paths are impossible to test.

3. Choose a baseline path consisting of false branches choices for each decision point.

4. Switch branch of 1 decision point to create an alternative path.

5. Repeat step 4 for all other decision points to obtain basis paths (Baseline + Alternative Paths).

6. Craft test inputs to test all identified basis paths.

Loops Considerations when dealing with loops:

• No Iteration skip the loop cycle entirely.
• 1 Iteration perform 1 iteration of loop cycle and then exit the loop cycle.

Cyclometric Complexity (CC)

CC computes the total no. of basis paths in a CFG:

• Method A: Edges $E$, Vertices $V$ in CFG:

$$\text{CC} = |E| + |V| + 2$$

• Method B: $D$ No. of binary decision points in CFG:

$$\text{CC} = D + 1$$