#vulnerable code 
                              @Test
  public void testSyncRefresh() throws IOException {
    initialize(HeaderCacheElement.TOKEN_STALENESS_MS + 1);
    Assert.assertEquals(CacheState.Good, underTest.headerCache.getCacheState());
    Assert.assertFalse(underTest.isRefreshing());
  } 
                            #location 4 
                            #vulnerability type UNSAFE_GUARDED_BY_ACCESS
#fixed code
                              @Test
  public void testSyncRefresh() throws IOException {
    Mockito.when(mockCredentials.refreshAccessToken()).thenReturn(
        new AccessToken("", new Date(HeaderCacheElement.TOKEN_STALENESS_MS + 1)));
    underTest = new RefreshingOAuth2CredentialsInterceptor(executorService, mockCredentials);
    Assert.assertEquals(CacheState.Expired, underTest.getCacheState());
    underTest.getHeaderSafe();
    Assert.assertNotEquals(CacheState.Exception, underTest.getCacheState());
    Assert.assertEquals(CacheState.Good, underTest.getCacheState());
    Assert.assertFalse(underTest.isRefreshing());
  }