//-------------------------------------------------------------------------
 public virtual void test_volatility()
 {
     for (int i = 0; i < NB_EXPIRY; i++)
     {
         double expiryTime = VOLS.relativeTime(TEST_EXPIRY[i]);
         for (int j = 0; j < NB_STRIKE; ++j)
         {
             double volExpected = SURFACE.zValue(expiryTime, TEST_STRIKE[j]);
             double volComputed = VOLS.volatility(CURRENCY_PAIR, TEST_EXPIRY[i], TEST_STRIKE[j], FORWARD[i]);
             assertEquals(volComputed, volExpected, TOLERANCE);
         }
     }
 }