MockCallback callback = new MockCallback("foo");
    Futures.addCallback(f, callback, ex);
    f.set("foo");
    assertEquals(1, ex.runCount);
  }

  // Error cases
  public void testSameThreadExecutionException() {
    SettableFuture<String> f = SettableFuture.create();
    Exception e = new IllegalArgumentException("foo not found");
    MockCallback callback = new MockCallback(e);