Integration testing is grey box testing method in which combined parts of an application is tested to determine whether all these functions works together. Let us learn this with an example.
Suppose your Drupal site sells online products and the shipment charge is set in such a way that it will be applicable to the product depending on the weight and destination. While doing the unit testing, tester has to test product selection, setting price,setting shipment to the destination etc separately. But in integration testing we test all these different functionality as a whole.