The issue was with ant configuration. From http://testautomationusingjunit.blogspot.com/2013/08/applying-rules-to-junit-tests-running.html, the target needs to be edited to contain JUnitCore in the classpath.
<target name="junit" depends="build">
<java classname="org.junit.runner.JUnitCore">
<classpath>
<path location="selenium_server/selenium-server-standalone-xxx.xx.jar"/>
</classpath>
</java>
<junit fork="no" haltonfailure="no" printsummary="true" failureProperty="test.failed" dir=".">
<test name="src.SampleTest" todir="./report" />
</junit>
</target>