@Test public void test() throws InterruptedException {
  MDCTestThread threadA=new MDCTestThread("a");
  threadA.start();
  MDCTestThread threadB=new MDCTestThread("b");
  threadB.start();
  threadA.join();
  threadB.join();
  assertNull(threadA.x0);
  assertEquals("a",threadA.x1);
  assertNull(threadA.x2);
  assertNull(threadB.x0);
  assertEquals("b",threadB.x1);
  assertNull(threadB.x2);
}
