@Test
public void testGetMostRecentIdReturnNull() {

    // Given
    when(memcacheService.get(MemcacheKey.DB_OPERATION_COUNTER.getName())).thenReturn(null);
    // when
    Long mostRecentId = operationService.getMostRecentId();
    // then
    verify(memcacheService).get(MemcacheKey.DB_OPERATION_COUNTER.getName());
    assertNull(mostRecentId);
}