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Java code coverage using cobertura

Code coverage is important as it gives developers confidence in the code that they are checking in. And for a startup automated test and measuring code coverage is equally important to be able to Ship early and be nimble.  I recently automated unit testing in jenkins and wanted to measure how much code coverage we have. So I integrated cobertura in the build framework. Cobertura is a build time instrumentation plugin so the steps are:

1) compile the code
2) Instrument the classes to generate instrumented classes with cobertura hooks.
3) modify junit class path to put instrumented classes before real classes
4) add a system property in junit ant task, so that cobertura knows where to write its statistics.
5) generate a coverage report in html to be used by developers
6) generate a coverage report in xml so that it can be published to sonar so we can do trends on code coverage release after release.

Here is how a typical code coverage report looks like http://cobertura.sourceforge.net/sample/



Here are some more details on the steps:

    <target name="instrument" description="Run Tests">
        <delete file="${basedir}/cobertura.ser" />
        <delete dir="${basedir}/build/instrumented-classes" />
        <cobertura-instrument todir="${basedir}/build/instrumented-classes">
            <ignore regex="org.apache.log4j.*" />
            <fileset dir="${basedir}/build/classes">
                <include name="**/*.class" />
                <exclude name="**/*Test.class" />
            </fileset>
        </cobertura-instrument>
    </target>


        <junit tempdir="${basedir}/build" printsummary="on"
               fork="yes"
               forkmode="perBatch"
               haltonfailure="true"
               failureproperty="tests.failed"
               showoutput="false">
            <jvmarg value="-Djava.awt.headless=true"/>
              <jvmarg value="-Djava.io.tmpdir=${basedir}/build/jenkinstest"/>
            <jvmarg value="-Dnet.sourceforge.cobertura.datafile=${basedir}/cobertura.ser" />           
            <classpath location="build/instrumented-classes" />
            <classpath refid="${testClasspathRefId}"/>
            <classpath refid="cobertura.classpath" />
            <formatter type="plain" usefile="false"/>
            <batchtest todir="${basedir}/${testReportsDir}">
                <fileset dir="${basedir}/${build}/classes">
                    <include name="**/*${testClassPattern}.*"/>
                    <exclude name="**/*$*.*"/>
                </fileset>
                <formatter type="xml"/>           
            </batchtest>
        </junit>


    <target name="coverage">
        <delete file="build/cobertura.ser" quiet="true" />
        <delete dir="build/coverage"  quiet="true"/>

        <cobertura-merge datafile= "build/cobertura.ser">
            <fileset dir="${basedir}/">
              <include name="**/cobertura.ser"/>
            </fileset>
        </cobertura-merge>   
        <cobertura-report format="html" destdir="build/coverage" datafile= "build/cobertura.ser">
            <fileset dir="${basedir}" includes="**/*.java"/>
        </cobertura-report>   
        <cobertura-report format="xml" destdir="build/coverage" datafile= "build/cobertura.ser">
            <fileset dir="${basedir}" includes="**/*.java"/>
        </cobertura-report>
        <cobertura-check haltonfailure="false" />
    </target>


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