Code Coverage with JaCoCo

JaCoCo (Java Code Coverage) is a lightweight library that tracks code paths executed during testing. It operates as a JVM agent that injects tracking instructions directly into compiled bytecode at runtime.

Branch vs Line Coverage

Line coverage tracks only if a line of code is entered. It can easily mask missing logical tests. Consider a single line conditional:

if (isActive && isVerified) { doTask(); }

If a test executes this line with isActive = true and isVerified = true, the line is fully covered. However, you have not tested what happens if isActive is false. Branch Coverage ensures all combinations of conditional paths are exercised.

Code Walkthrough

Here is a method requiring multiple test branches to achieve 100% branch coverage.

public class CoverageDemo {
public int calculateDiscount(int price, boolean premiumMember) {
        if (premiumMember && price > 100) {
            return (int) (price * 0.8);
        }
        return price;
    }
}

Interview-Relevant Information