@Override
  public <T extends Serializable> T getCachedValue(String idempotentId)
      throws IllegalArgumentException {
    if (!knownValues.containsKey(idempotentId)) {
      throw new IllegalArgumentException(
          idempotentId
              + " is not a known key, known keys: "
              + Joiner.on(", ").join(knownValues.keySet()));
    }
    return (T) knownValues.get(idempotentId);
  }
@Test
  public void getCachedValue() throws Exception {
    googleExecutor.setJobId(JOB_ID);
    googleExecutor.executeAndSwallowIOExceptions("id1", ITEM_NAME, () -> "idempotentId1");
    assertEquals(googleExecutor.getCachedValue("id1"), "idempotentId1");
  }