JarCastingjacoco-badge-maven-plugin 
A simple maven plugin to generate JaCoCo build badges
Configuration
Before we can generate a JaCoCo test coverage badge, we need to run JaCoCo test coverage!
JaCoCo measures test coverage of surefire unit tests and failsafe integration tests. Both cases require that JaCoCo be configured to integrate directly with the plugin in question.
Configuring JaCoCo for Unit Tests
Here is a simple setup for surefire and JaCoCo that generates a formatted HTML JaCoCo test coverage report.
<!-- Set up surefire to run just unit tests and take
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.15</version>
<configuration>
<argLine>${surefireArgLine}</argLine>
<skipTests>${skip.unit.tests}</skipTests>
<excludes>
<!-- Standard approach to excluding integration tests -->
<exclude>**/IT*.java</exclude>
</excludes>
</configuration>
</plugin>
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>0.8.0</version>
<configuration>
<excludes>
<!-- Any exclusions you require, *.class -->
</excludes>
</configuration>
<executions>
<!-- Ask JaCoCo to generate a test report from surefire tests -->
<execution>
<id>prepare-code-coverage</id>
<goals>
<goal>prepare-agent</goal>
</goals>
<configuration>
<propertyName>surefireArgLine</propertyName>
</configuration>
</execution>
<!-- Ask JaCoCo to format test report into browsable HTML -->
<!-- Multi-module builds should include report-aggregate and use the -->
<!-- default outputDirectory. -->
<!-- Single-module builds should exclude report-aggregate and use -->
<!-- the given outputDirectory. -->
<execution>
<id>report-code-coverage</id>
<goals>
<goal>report</goal>
<!-- <goal>report-aggregate</goal> -->
</goals>
<configuration>
<!-- Multi-module builds should
<outputDirectory>${project.reporting.outputDirectory}/jacoco-aggregate</outputDirectory>
</configuration>
</execution>
<!-- Make sure we have at least 70% coverage -->
<execution>
<id>verify-test-coverage</id>
<goals>
<goal>check</goal>
</goals>
<configuration>
<rules>
<rule>
<element>BUNDLE</element>
<excludes>
<exclude>*Mojo</exclude>
</excludes>
<limits>
<limit>
<counter>INSTRUCTION</counter>
<value>COVEREDRATIO</value>
<minimum>70%</minimum>
</limit>
</limits>
</rule>
</rules>
<outputDirectory>${project.reporting.outputDirectory}/jacoco-aggregate</outputDirectory>
</configuration>
</execution>
</executions>
</plugin>
With this configuration, running mvn test should generate a friendly HTML report of test coverage at target/site/jacoco-aggregate/index.html.
Configuring Badge Generation
Once JaCoCo has been configured to generate a formatted report, it's time to generate a badge from that report. Here is an example configuration of this plugin to generate a badge based on unit tests:
<plugin>
<groupId>com.sigpwned</groupId>
<artifactId>jacoco-badge-maven-plugin</artifactId>
<version>0.1.3</version>
<executions>
<execution>
<id>generate-jacoco-badge</id>
<phase>verify</phase>
<goals>
<goal>badge</goal> <!-- Generate a badge from a unified JaCoCo report -->
</goals>
<configuration>
<!-- What coverage level is considered passing? Optional, default 70. -->
<passing>70</passing>
<!-- Legal values: instruction, branch, line, method. Optional, default instruction. -->
<metric>instruction</metric>
</configuration>
</execution>
</executions>
</plugin>
Including the Badge in your README
There are a couple of good ways to include the badge file into your README:
-
GitHub Only -- Generate the badge file into a resource directory, and then embed a reference to the badge into your README. This has the benefit of being very simple, but won't allow for the testing of pull requests, etc. For an example, look at this README.
-
CodeBuild -- Save the generated badge file as an artifact; configure S3 to send an event every time a badge is uploaded; use a lambda function to copy the latest badge to a known, fixed location; embed a link to that fixed location.