Coverage reports in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

JUnit Coverage Report Output

Given the following JUnit test and code, what will the coverage report indicate for the method calculateSum?

JUnit

public class Calculator {
    public int calculateSum(int a, int b) {
        if (a > 0 && b > 0) {
            return a + b;
        } else {
            return 0;
        }
    }
}

import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;

public class CalculatorTest {
    @Test
    public void testCalculateSumPositive() {
        Calculator calc = new Calculator();
        assertEquals(5, calc.calculateSum(2, 3));
    }
}

A 50% method coverage, 50% branch coverage

B 100% method coverage, 100% branch coverage

C 100% method coverage, 50% branch coverage

D 50% method coverage, 100% branch coverage

💡 Hint

Think about which parts of the method are executed by the test inputs.

The test calls calculateSum with positive numbers, so the 'if' branch is taken, but the 'else' branch is not. The method is fully executed, so method coverage is 100%, but branch coverage is only 50% because one branch is not tested.

❓ assertion

intermediate

Assertion for Coverage Threshold

Which JUnit assertion correctly checks that the code coverage percentage is at least 80%?

JUnit

double coveragePercentage = 75.5;

A assertTrue(coveragePercentage >= 80);

B assertEquals(coveragePercentage, 80);

C assertFalse(coveragePercentage < 80);

D assertNotNull(coveragePercentage >= 80);

💡 Hint

Use an assertion that checks a condition is true.

assertTrue checks if the condition is true. Here, it verifies coveragePercentage is at least 80. assertEquals checks equality, which is not what we want. assertFalse would invert the condition, and assertNotNull is for objects, not booleans.

🧠 Conceptual

advanced

Understanding Coverage Report Metrics

Which statement best describes the difference between line coverage and branch coverage in a JUnit coverage report?

A Line coverage measures executed methods; branch coverage measures executed classes.

B Line coverage measures executed classes; branch coverage measures executed methods.

C Line coverage measures executed branches; branch coverage measures executed lines.

D Line coverage measures executed lines; branch coverage measures executed decision paths.

💡 Hint

Think about what a branch means in code.

Line coverage counts how many lines of code ran. Branch coverage counts how many possible paths (like if-else decisions) were taken during tests.

🔧 Debug

advanced

Debugging Missing Coverage

A JUnit coverage report shows 0% coverage for a method, but the test suite runs without errors. What is the most likely cause?

A The method is never called by any test.

B The test suite has syntax errors.

C The coverage tool is not installed.

D The method is private and cannot be tested.

💡 Hint

Think about what coverage means.

Coverage measures which code runs during tests. If a method is never called, coverage is zero even if tests pass. Syntax errors or missing tools would cause test failures or no report. Private methods can be covered if called indirectly.

❓ framework

expert

Configuring Coverage Thresholds in JUnit

Which configuration snippet correctly sets a minimum branch coverage threshold of 85% using JaCoCo in a Maven project for JUnit tests?

JUnit

<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.8.8</version>
  <executions>
    <execution>
      <goals>
        <goal>prepare-agent</goal>
      </goals>
    </execution>
    <execution>
      <id>report</id>
      <phase>test</phase>
      <goals>
        <goal>report</goal>
      </goals>
    </execution>
    <execution>
      <id>check</id>
      <goals>
        <goal>check</goal>
      </goals>
      <configuration>
        <!-- Threshold config here -->
      </configuration>
    </execution>
  </executions>
</plugin>

A

<rules>
  <rule>
    <element>CLASS</element>
    <limits>
      <limit>
        <counter>LINE</counter>
        <value>COVEREDRATIO</value>
        <minimum>0.85</minimum>
      </limit>
    </limits>
  </rule>
</rules>

B

<rules>
  <rule>
    <element>BUNDLE</element>
    <limits>
      <limit>
        <counter>BRANCH</counter>
        <value>COVEREDRATIO</value>
        <minimum>0.85</minimum>
      </limit>
    </limits>
  </rule>
</rules>

C

<rules>
  <rule>
    <element>METHOD</element>
    <limits>
      <limit>
        <counter>INSTRUCTION</counter>
        <value>COVEREDRATIO</value>
        <minimum>0.85</minimum>
      </limit>
    </limits>
  </rule>
</rules>

D

<rules>
  <rule>
    <element>BUNDLE</element>
    <limits>
      <limit>
        <counter>LINE</counter>
        <value>COVEREDRATIO</value>
        <minimum>0.85</minimum>
      </limit>
    </limits>
  </rule>
</rules>

💡 Hint

Branch coverage uses the BRANCH counter and is usually set at the BUNDLE level.

To enforce branch coverage threshold, the counter must be BRANCH and element BUNDLE. Other options set thresholds for line or instruction coverage or at different element levels.