fix(core): Add OrderTestingService to core exports (#1469)

packages/core/src/service/index.ts

@@ -31,6 +31,7 @@ export * from './services/fulfillment.service';
 export * from './services/global-settings.service';
 export * from './services/history.service';
 export * from './services/order.service';
+export * from './services/order-testing.service';
 export * from './services/payment-method.service';
 export * from './services/payment.service';
 export * from './services/product-option-group.service';