How to enable code coverage report using JaCoCo, Maven and Jenkins

 

What is Code Coverage?

Code coverage is the percentage of code which is covered by automated tests. Code coverage measurement simply determines which statements in a body of code have been executed through a test run, and which statements have not. In general, a code coverage system collects information about the running program and then combines that with source information to generate a report on the test suite's code coverage.

Code coverage is part of a feedback loop in the development process. As tests are developed, code coverage highlights aspects of the code which may not be adequately tested and which require additional testing. This loop will continue until coverage meets some specified target.

Why Measure Code Coverage?

It is well understood that unit testing improves the quality and predictability of your software releases. Do you know, however, how well your unit tests actually test your code? How many tests are enough? Do you need more tests? These are the questions code coverage measurement seeks to answer.

Coverage measurement also helps to avoid test entropy. As your code goes through multiple release cycles, there can be a tendency for unit tests to atrophy. As new code is added, it may not meet the same testing standards you put in place when the project was first released. Measuring code coverage can keep your testing up to the standards you require. You can be confident that when you go into production there will be minimal problems because you know the code not only passes its tests but that it is well tested.

In summary, we measure code coverage for the following reasons:

• To know how well our tests actually test our code
• To know whether we have enough testing in place
• To maintain the test quality over the lifecycle of a project

Code coverage is not a panacea. Coverage generally follows an 80-20 rule. Increasing coverage values becomes difficult, with new tests delivering less and less incrementally. If you follow defensive programming principles, where failure conditions are often checked at many levels in your software, some code can be very difficult to reach with practical levels of testing. Coverage measurement is not a replacement for good code review and good programming practices.

In general you should adopt a sensible coverage target and aim for even coverage across all of the modules that make up your code. Relying on a single overall coverage figure can hide large gaps in coverage.

Code coverage is important aspect for maintaining quality. There are different ways to manage code quality. one of the effective ways is to measure code coverage by using plug-ins such as JaCoCo, Cobertura.

We will see how to enable code coverage for your Java project and view coverage report in Jenkins UI.

step # 1: Add Maven JaCoCo plugin in POM.xml under <finalName>MyWebApp</finalName> in your project pom.xml

<plugins>
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>0.7.7.201606060606</version>
<executions>
<execution>
<id>jacoco-initialize</id>
<goals>
<goal>prepare-agent</goal>
</goals>
</execution>
<execution>
<id>jacoco-report</id>
<phase>test</phase>
<goals>
<goal>report</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>

It should look similar to below:

Step 2 : Add JaCoCo plug-in in Jenkins:

Step 3:

For Freestyle Job:
Enable in Jenkins job to view code coverage report by going to post build action and add Record JaCoCo coverage report

Step 4 : Run the job by clicking Build now

Step 5:
 Click on the job to view code coverage report.