I'm focusing on the new Test Flight procedure. I developed an application (that I submitted through Xcode to the iTunes Connect portal) that crashes if a UIButton is tapped. Since, the application is available for Beta Testing to Internal Testers, I would expect to see a crash log within the new Crashes section of Xcode 6.3 Beta 4 (see Crashes Organizer Help). But nothing. No crashes available.
Is there any particular reason for that? Is this related to the type of testers I'm using? I'm understanding that Xcode 6.3 is Beta version.
Update
Xcode 6.3 has been released and crashes are now available.
Original answer
From Apple documentation
How Crash Logs Are Collected and Aggregated into Crash Reports
Apple provides a service that collects crash logs from users and organizes them into downloadable crash reports. However, crash logs are collected only if you upload an app with the symbols. (In the Archives organizer, select the “Include app symbols for your application…” box when you upload your app to iTunes Connect.) For apps released in the App Store, the user must also agree to share crash logs with developers. TestFlight users automatically share crash logs with developers. The service that creates the crash reports does the following:
Collects crash logs from both TestFlight and App Store builds
Provides the total number of unique devices where the crash occurred
Provides a sample set of crash logs for each crash report
Removes all personal user data from the crash logs
Creates crash reports daily
When you open the Crashes organizer, Xcode begins refreshing the crash reports for your apps. Xcode downloads the top crash reports—crash reports with the most number of occurrences on unique devices—that occurred during the past two weeks. However, there may be up to a three day delay between when you first distribute your app and when crash reports are available in Xcode.
where emphasis is mine.
So I guess I need to wait.