Map<String, String> variables = new HashMap<String, String>();
ReplaceStringWithFunctions transformer = new ReplaceStringWithFunctions(new CompoundVariable(), variables);
jmctx.setVariables(new JMeterVariables());
StringProperty prop = new StringProperty(LoopController.LOOPS,"${__Random(1,12,)}");
JMeterProperty newProp = transformer.transformValue(prop);
newProp.setRunningVersion(true);
loop.setProperty(newProp);
loop.addTestElement(new TestSampler("random run"));
loop.setRunningVersion(true);