Coverage reports in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to generate a coverage report using JaCoCo in a Maven project.

JUnit

<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.8.8</version>
  <executions>
    <execution>
      <goals>
        <goal>[1]</goal>
      </goals>
    </execution>
  </executions>
</plugin>

Drag options to blanks, or click blank then click option'

Apackage

Bcompile

Ctest

Dprepare-agent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'test' instead of 'prepare-agent' causes no coverage data to be collected.

Using 'compile' or 'package' does not start the coverage agent.

The prepare-agent goal sets up the JaCoCo agent to collect coverage data during tests.

2fill in blank

medium

Complete the code to generate the coverage report after tests run.

JUnit

<execution>
  <id>report</id>
  <phase>[1]</phase>
  <goals>
    <goal>report</goal>
  </goals>
</execution>

Drag options to blanks, or click blank then click option'

Atest

Bcompile

Cverify

Dinstall

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'test' phase generates report too early before tests finish.

Using 'compile' phase is before tests run.

The verify phase runs after tests and is the right time to generate the coverage report.

3fill in blank

hard

Fix the error in the JaCoCo plugin configuration to correctly bind the report goal.

JUnit

<execution>
  <id>default-report</id>
  <phase>[1]</phase>
  <goals>
    <goal>report</goal>
  </goals>
</execution>

Drag options to blanks, or click blank then click option'

Averify

Bprepare-package

Ctest

Dcompile

Attempts:

3 left

💡 Hint

Common Mistakes

Binding to 'test' phase causes report generation before tests finish.

Binding to 'compile' phase is before tests run.

The verify phase is the correct lifecycle phase to bind the report goal for coverage reports.

4fill in blank

hard

Fill both blanks to create a JaCoCo report that includes XML and HTML formats.

JUnit

<configuration>
  <formats>
    <format>[1]</format>
    <format>[2]</format>
  </formats>
</configuration>

Drag options to blanks, or click blank then click option'

Axml

Bcsv

Chtml

Dtxt

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'csv' or 'txt' causes errors as they are unsupported formats.

Using only one format misses the other common report type.

JaCoCo supports xml and html formats for coverage reports.

5fill in blank

hard

Fill all three blanks to configure JaCoCo to fail the build if coverage is below 80%.

JUnit

<configuration>
  <rules>
    <rule>
      <element>[1]</element>
      <limits>
        <limit>
          <counter>[2]</counter>
          <value>[3]</value>
          <minimum>0.80</minimum>
        </limit>
      </limits>
    </rule>
  </rules>
</configuration>

Drag options to blanks, or click blank then click option'

ACLASS

BLINE

CINSTRUCTION

DCOVEREDRATIO

Attempts:

3 left

💡 Hint

Common Mistakes

Using unsupported elements or counters causes configuration errors.

Setting minimum above 1.0 or below 0 causes invalid rules.

The element is set to CLASS to check coverage per class, the counter is LINE to measure line coverage, and the value is COVEREDRATIO to specify the coverage ratio metric.

This configuration ensures the build fails if line coverage is below 80%.

Practice

1. What is the main purpose of a coverage report in JUnit testing?

easy

A. To show which parts of the code were executed during tests

B. To list all test cases in the project

C. To measure the speed of test execution

D. To generate test data automatically

Solution

1. Step 1: Understand coverage report purpose

   A coverage report shows which lines or branches of code were run during testing.

2. Step 2: Compare options to definition

   Only To show which parts of the code were executed during tests matches this purpose; others describe unrelated features.

3. Final Answer:

   To show which parts of the code were executed during tests -> Option A

4. Quick Check:

   Coverage report = executed code lines [OK]

Hint: Coverage reports highlight tested code lines quickly [OK]

Common Mistakes:

• Confusing coverage with test case listing
• Thinking coverage measures test speed
• Assuming coverage generates test data

2. Which tool is commonly used with JUnit to generate coverage reports?

easy

A. JaCoCo

B. JUnitParams

C. Mockito

D. Selenium

Solution

1. Step 1: Identify coverage tools for JUnit

   JaCoCo is a popular Java code coverage tool that integrates with JUnit.

2. Step 2: Eliminate unrelated tools

   Selenium is for UI testing, Mockito for mocking, JUnitParams for parameterized tests, not coverage.

3. Final Answer:

   JaCoCo -> Option A

4. Quick Check:

   Coverage tool with JUnit = JaCoCo [OK]

Hint: JaCoCo is the go-to coverage tool for Java tests [OK]

Common Mistakes:

• Confusing Selenium with coverage tools
• Mixing mocking frameworks with coverage
• Assuming JUnitParams generates coverage

3. Given this JaCoCo coverage summary:
Lines covered: 80
Lines missed: 20
What is the coverage percentage?

medium

A. 100%

B. 20%

C. 80%

D. 60%

Solution

1. Step 1: Calculate total lines

   Total lines = covered + missed = 80 + 20 = 100 lines.

2. Step 2: Calculate coverage percentage

   Coverage % = (covered / total) * 100 = (80 / 100) * 100 = 80%.

3. Final Answer:

   80% -> Option C

4. Quick Check:

   80 covered of 100 total = 80% [OK]

Hint: Coverage % = covered lines ÷ total lines x 100 [OK]

Common Mistakes:

• Using missed lines as coverage
• Forgetting to add covered and missed for total
• Mixing up numerator and denominator

4. You ran tests with JaCoCo but the coverage report shows 0% coverage. What is the most likely cause?

medium

A. Tests did not execute any code

B. JaCoCo was not properly attached to the test run

C. All tests passed successfully

D. The source code is empty

Solution

1. Step 1: Analyze 0% coverage meaning

   0% coverage means no code was recorded as executed during tests.

2. Step 2: Identify common causes

   If tests ran but coverage is zero, JaCoCo likely was not attached or configured correctly.

3. Final Answer:

   JaCoCo was not properly attached to the test run -> Option B

4. Quick Check:

   0% coverage usually means missing JaCoCo setup [OK]

Hint: Check JaCoCo setup if coverage is zero [OK]

Common Mistakes:

• Assuming tests passed means coverage is full
• Thinking empty source code is common
• Ignoring JaCoCo configuration errors

5. You want to improve your test coverage report by including branch coverage in JaCoCo. Which configuration change is needed?

hard

A. Increase the number of test classes

B. Add @BranchCoverage annotation to test methods

C. Use a different testing framework instead of JUnit

D. Enable branchCoverage option in JaCoCo plugin settings

Solution

1. Step 1: Understand branch coverage

   Branch coverage measures if all decision branches (like if/else) are tested.

2. Step 2: Configure JaCoCo for branch coverage

   JaCoCo supports branch coverage via plugin settings; enabling branchCoverage activates it.

3. Step 3: Eliminate incorrect options

   No annotation @BranchCoverage exists; changing framework or test count doesn't enable branch coverage reporting.

4. Final Answer:

   Enable branchCoverage option in JaCoCo plugin settings -> Option D

5. Quick Check:

   Branch coverage = enable in JaCoCo config [OK]

Hint: Enable branchCoverage in JaCoCo config to track branches [OK]

Common Mistakes:

• Looking for annotations to enable coverage
• Thinking more tests auto-enable branch coverage
• Switching frameworks unnecessarily