<target name="testClass">
    <echo message="Run All Local Tests in ${what} in org '${sf.branch.username}' (no deployment)." />
    <sf:deploy  username="${sf.branch.username}"    password="${sf.branch.password}"
                sessionId="${sf.sessionId}"         serverurl="${sf.branch.serverurl}"
                maxPoll="${sf.maxPoll}"             pollWaitMillis="20000"
                deployRoot="putFSTest"          rollbackOnError="true"  testlevel="RunSpecifiedTests">
        <runTest>${what}</runTest>
    </sf:deploy>
</target>

ant testClass -Dwhat=MyTestClass