public void yValue() {
   for (int i = 0; i < NB_X_SAMPLE; i++) {
     double yComputed = ADD_FIXED_CURVE.yValue(X_SAMPLE[i]);
     double yExpected = FIXED_CURVE.yValue(X_SAMPLE[i]) + SPREAD_CURVE.yValue(X_SAMPLE[i]);
     assertEquals(yComputed, yExpected, TOLERANCE_Y);
   }
 }