JaCoCo setup and configuration in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to apply the JaCoCo plugin in a Gradle build script.

JUnit

plugins {
    id '[1]'
}

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

Amaven

Bjava

Capplication

Djacoco

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'java' instead of 'jacoco' as plugin id.

Forgetting to add the plugin block.

The JaCoCo plugin is applied in Gradle using id 'jacoco'.

2fill in blank

medium

Complete the code to set the JaCoCo tool version in Gradle.

JUnit

jacoco {
    toolVersion = '[1]'
}

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

A0.8.7

B1.0.0

C0.7.5

D2.0.1

Attempts:

3 left

💡 Hint

Common Mistakes

Using an invalid or non-existent version number.

Omitting the toolVersion setting.

Setting toolVersion to a valid JaCoCo version like 0.8.7 ensures compatibility.

3fill in blank

hard

Fix the error in the test task configuration to generate JaCoCo reports.

JUnit

tasks.test {
    useJUnitPlatform()
    finalizedBy('[1]')
}

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

AgenerateReport

BtestReport

CjacocoTestReport

DcoverageReport

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent task name in finalizedBy.

Forgetting to link the report generation task.

The finalizedBy should reference the jacocoTestReport task to generate coverage reports after tests.

4fill in blank

hard

Fill both blanks to configure the JaCoCo report formats in Gradle.

JUnit

jacocoTestReport {
    reports {
        xml.required = [1]
        html.required = [2]
    }
}

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

Atrue

Bfalse

Cnull

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using false disables the report format.

Using null or 0 causes errors.

Setting both xml.required and html.required to true enables those report formats.

5fill in blank

hard

Fill all three blanks to exclude generated classes from JaCoCo coverage.

JUnit

jacocoTestReport {
    afterEvaluate {
        classDirectories.setFrom(files(classDirectories.files.collect { file ->
            fileTree(dir: file, exclude: [[1], [2], [3]])
        }))
    }
}

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

A'**/R.class'

B'**/BuildConfig.class'

C'**/Manifest.class'

D'**/Main.class'

Attempts:

3 left

💡 Hint

Common Mistakes

Including main classes in the exclude list.

Using incorrect patterns for exclusion.

Excluding generated classes like R.class, BuildConfig.class, and Manifest.class avoids counting them in coverage.

Practice

1. What is the primary purpose of JaCoCo in a JUnit testing environment?

easy

A. To replace JUnit as a testing framework

B. To run JUnit tests faster

C. To generate test data automatically

D. To measure how much of your code is tested by your unit tests

Solution

1. Step 1: Understand JaCoCo's role

   JaCoCo is a code coverage tool that tracks which parts of your code are executed during tests.

2. Step 2: Compare options

   Only To measure how much of your code is tested by your unit tests correctly describes JaCoCo's purpose; others describe unrelated functions.

3. Final Answer:

   To measure how much of your code is tested by your unit tests -> Option D

4. Quick Check:

   JaCoCo = Code coverage tool [OK]

Hint: JaCoCo measures tested code coverage, not test speed [OK]

Common Mistakes:

• Confusing JaCoCo with test runners
• Thinking JaCoCo generates tests
• Assuming JaCoCo replaces JUnit

2. Which of the following is the correct way to add JaCoCo plugin in a Maven pom.xml file?

easy

A.
org.jacoco
jacoco-maven-plugin
0.8.8

B.
org.junit.jupiter
junit-jupiter-engine
5.9.2

C.
org.jacoco
jacoco-core
0.8.8

D.
org.apache.maven.plugins
maven-compiler-plugin
3.8.1

Solution

1. Step 1: Identify JaCoCo plugin syntax

   JaCoCo is added as a Maven plugin with groupId 'org.jacoco' and artifactId 'jacoco-maven-plugin'.

2. Step 2: Eliminate incorrect options

   Options B and D are unrelated plugins; A is a dependency, not a plugin.

3. Final Answer:

   Correct JaCoCo plugin configuration in Maven -> Option A

4. Quick Check:

   JaCoCo plugin = org.jacoco:jacoco-maven-plugin [OK]

Hint: JaCoCo is a plugin, not a dependency in Maven [OK]

Common Mistakes:

• Adding JaCoCo as a dependency instead of plugin
• Confusing JUnit plugin with JaCoCo plugin
• Using unrelated Maven plugins

3. Given the following JaCoCo configuration snippet in a Maven pom.xml:

<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>
  </executions>
</plugin>

What will happen when you run mvn test?

medium

A. JaCoCo agent prepares coverage data before tests, then generates a coverage report after tests

B. Tests will run without coverage data collection

C. The build will fail due to missing report goal

D. JaCoCo will only generate a report without running tests

Solution

1. Step 1: Understand prepare-agent goal

   The 'prepare-agent' goal sets up JaCoCo to collect coverage data during test execution.

2. Step 2: Understand report goal in test phase

   The 'report' goal runs after tests to generate the coverage report.

3. Final Answer:

   JaCoCo collects coverage during tests and generates report after -> Option A

4. Quick Check:

   prepare-agent + report = coverage data + report [OK]

Hint: prepare-agent collects data; report generates coverage output [OK]

Common Mistakes:

• Assuming coverage is collected without prepare-agent
• Thinking report runs before tests
• Confusing goals causing build failure

4. You added JaCoCo plugin to your Maven project but no coverage report is generated after running mvn test. What is the most likely cause?

medium

A. JUnit tests are not written correctly

B. You used an incorrect JaCoCo version number

C. You forgot to bind the report goal to the test phase

D. Maven compiler plugin is missing

Solution

1. Step 1: Check JaCoCo execution bindings

   Without binding the 'report' goal to the 'test' phase, JaCoCo won't generate reports automatically.

2. Step 2: Eliminate other causes

   Incorrect version usually causes build errors; test correctness or compiler plugin absence won't stop report generation if configured.

3. Final Answer:

   Missing binding of report goal to test phase -> Option C

4. Quick Check:

   Report goal must be bound to test phase [OK]

Hint: Bind report goal to test phase to generate coverage report [OK]

Common Mistakes:

• Ignoring execution phase bindings
• Blaming test code for missing reports
• Assuming version mismatch causes silent failure

5. You want to configure JaCoCo in a Gradle project to generate an XML coverage report after tests run. Which snippet correctly configures this in build.gradle?

hard

A. jacocoTestReport {
reports {
xml.required = true
html.required = false
}
}

B. jacocoTestReport {
reports {
xml.enabled = true
html.enabled = true
}
}

C. test {
useJUnitPlatform()
jacoco {
xml.enabled = true
}
}

D. jacoco {
toolVersion = '0.8.8'
reports {
xml.enabled = true
}
}

Solution

1. Step 1: Identify correct JaCoCo Gradle report syntax

   The 'jacocoTestReport' task configures reports with 'xml.enabled' and 'html.enabled' properties.

2. Step 2: Compare options for XML report generation

   jacocoTestReport { reports { xml.enabled = true html.enabled = true } } correctly enables XML report; the snippet using 'required' properties is outdated; others configure in wrong blocks.

3. Final Answer:

   jacocoTestReport with reports { xml.enabled = true } -> Option B

4. Quick Check:

   Use xml.enabled = true in jacocoTestReport [OK]

Hint: Use xml.enabled = true inside jacocoTestReport for XML reports [OK]

Common Mistakes:

• Using xml.required instead of xml.enabled
• Configuring jacoco block instead of jacocoTestReport
• Missing enabling of reports