Well it has been a year since Facebook bought WhatsApp and we saw no integration of any sort until now. Facebook has begun testing a new feature in its Facebook for Android app (Version 188.8.131.52.13) that includes the first major integration of WhatsApp. The sources shows how the integration would look.
As you can see in the above images, they are working on the addition of the WhatsApp’s send icon where the like and share buttons are already there. There are reports of features which will allow the sending of instant messages between Facebook Messenger and WhatsApp. These are among the first changes we have seen since the merger and while we have not found any details about when can we see these changes live or available to public.