How can I send an iOS app to someone to test?

Do the following steps:

1. Take the UDID of your customer's iOS Device (Search Google for how to get the UDID of the Device)
2. Add that UDID to the Apple's Developer Portal
3. Generate the new development or AdHoc provisioning Profile with that new UDID included in it.
4. Use that new profile and generate the Application Build.
5. Then save it for adhoc purpose and you will get the IPA file. You can send that file either to client or you can upload that IPA file to Diawi or Apple testflight (Testflight App)