@Test
 public void ensureHealthy_happyDay_whenWithinLimit() throws Exception {
   final int limit = 10;
   when(pool.getEvictAfterNumberOfUse()).thenReturn(limit);
   ensureHealthy_happyDay(limit);
   // no exception should have thrown
 }
 @Test
 public void ensureHealthy_chokes_whenOutOfLimit() throws Exception {
   final int limit = 10;
   when(pool.getEvictAfterNumberOfUse()).thenReturn(limit);
   exception.expect(GMServiceException.class);
   ensureHealthy_happyDay(limit + 1);
 }
 @Test
 public void ensureHealthy_happyDay_onNoLimit() throws Exception {
   when(pool.getEvictAfterNumberOfUse()).thenReturn(0);
   ensureHealthy_happyDay(10);
   // no exception should have thrown
 }