Basic Block Coverage

software-engineering testing

Definition

Basic Block Coverage

Basic Block Coverage is a structural testing metric that measures the percentage of basic blocks in the Control Flow Graph that have been executed at least once.

Calculation Note: When counting the “Total number of blocks,” we exclude the special Entry and Exit blocks. We only count the blocks containing actual code statements.

Equivalence to Statement Coverage

In this course (and many tools), Basic Block Coverage is used as the practical definition of Statement Coverage.

Reasoning: A basic block is a sequence of instructions with a single entry and single exit. If the block is entered, all statements within it are executed. Therefore, covering all blocks implies covering all statements.
Difference: The calculation denominator differs (Blocks vs. Statements vs. Lines), but the coverage goal (executing the code) is identical.

Example

Consider the absoluteSum method:

graph TD
    Entry((Entry)) --> B1["BB<sub>1</sub>: sum = 0"]
    B1 --> b1{"BB<sub>2</sub>: b<sub>1</sub> = x < 0"}
    b1 -- "True" --> B3["BB<sub>3</sub>: x = -x"]
    b1 -- "False" --> b2{"BB<sub>4</sub>: b<sub>2</sub> = y < 0"}
    B3 --> b2
    b2 -- "True" --> B5["BB<sub>5</sub>: y = -y"]
    b2 -- "False" --> B6["BB<sub>6</sub>: sum = x + y"]
    B5 --> B6
    B6 --> Exit((Exit))

To achieve 100% Basic Block Coverage, we must execute blocks BB_1 through BB_6.

Total Blocks: 6 (exclude Entry and Exit).
Test Case: $x = - 1, y = - 1$
Path: Entry $\to B B_{1} \to B B_{2} \to B B_{3} \to B B_{4} \to B B_{5} \to B B_{6} \to$ Exit
Result: 6/6 Blocks Executed (100%).