Ant and Jacoco: Need to set junit's fork to “true” but not property that's true

Question

I'm using the Jacoco Junit task and tried the following:

    <!-- run the junit tests -->
    <echo>DEBUG: $${junit.fork} = "${junit.fork}"</echo>
    <jacoco:coverage
        destfile="${target.dir}/jacoco.exec"
        append="false">
        <junit fork="${junit.fork}" includeAntRuntime="true">
            <classpath>
                <pathelement path="${main.destdir}"/>
                <pathelement path="${test.destdir}"/>
            </classpath>
            <classpath refid="test.classpath"/>
            <formatter type="${junit.formatter.type}"/>
            <batchtest      todir="${junit.batchtest.todir}">
                <fileset dir="${test.destdir}" />
            </batchtest>
        </junit>
    </jacoco:coverage>

And got the following:

test:
     [echo] DEBUG: ${junit.fork} = "true"
[jacoco:coverage] Enhancing junit with coverage

BUILD FAILED
D:\build.xml:233: Coverage can only be applied on a forked VM

Total time: 6 seconds

D:\>

As you can see, ${junit.fork} property was set to true, and I used that property in <junit fork="${junit.fork}"/>.

However, instead of using that property, I simply set <junit fork="true">, it works fine:

    <jacoco:coverage
        destfile="${target.dir}/jacoco.exec"
        append="false">
        <junit fork="true" includeAntRuntime="true">
            <classpath>
                <pathelement path="${main.destdir}"/>
                <pathelement path="${test.destdir}"/>
            </classpath>
            <classpath refid="test.classpath"/>
            <formatter type="${junit.formatter.type}"/>
            <batchtest      todir="${junit.batchtest.todir}">
                <fileset dir="${test.destdir}" />
            </batchtest>
        </junit>
    </jacoco:coverage>

I have run ant -d test to verify that the Java JVM is forking when I use the ${junit.fork} property.

Why is JaCoCo insisting that the JUnit test isn't being forked unless I set the fork parameter to the string true and not to a property that's equals true?

Answer 1

According to the Jacoco coverage task source code :

...
public void enhanceTask(final Task task) {
    final RuntimeConfigurable configurableWrapper = task.getRuntimeConfigurableWrapper();

    final String forkValue = (String) configurableWrapper.getAttributeMap().get("fork");
    if (!Project.toBoolean(forkValue)) {
        throw new BuildException("Coverage can only be applied on a forked VM", getLocation());
    }
    addJvmArgs(task);
}
...

The forkValue is read from the configurableWrapper. The attribute map values (like ${junit.fork}) are evalutated using the method RuntimeConfigurable.maybeConfigure which is invoked by Task.mayBeConfigure. And when you continue to look at the Jacoco source code :

...
public void addTask(final Task task) {
    if (childTask != null) {
        throw new BuildException("Only one child task can be supplied to the coverge task", getLocation());
    }
    this.childTask = task;
    final String subTaskTypeName = task.getTaskType();
    final TaskEnhancer enhancer = findEnhancerForTask(subTaskTypeName);
    if (enhancer == null) {
        throw new BuildException(format("%s is not a valid child of the coverage task", subTaskTypeName), getLocation());
}
    if (isEnabled()) {
        log(format("Enhancing %s with coverage", childTask.getTaskName()));
        enhancer.enhanceTask(task);
    }
    task.maybeConfigure();
}
...

This method (mayBeConfigure) is invoked after the task has been enhanced (enhancer.enhanceTask(task);). I guess that it is your problem and a bug... and we should report it to the jacoco bug tracker.

Jacoco issue