WroTestUtils.runConcurrently(new ContextPropagatingCallable<Void>(new Callable<Void>() {
public Void call()
throws Exception {
Context.set(Context.standaloneContext());
final Reader reader = new StringReader("@import('/path/to/imported');");
final Resource resource1 = Resource.create("resource1.css");
final Resource resource2 = Resource.create("resource2.css");
if (new Random().nextBoolean()) {
victim.process(resource1, reader, new StringWriter());
} else {
victim.process(resource2, reader, new StringWriter());
}