AAA debugs are by far the easiest and most common mechanism for troubleshooting AAA issues. Although you can use show commands to check the various stages a negotiation is in, debugs are by far the best sources of information for failing AAA setups.
AAA show Commands
AAA show commands are often used in conjunction with debug commands and play a supporting role to the debug commands. However, they can often be used to gather summary information about the status of the AAA features and the TACACS+ and RADIUS feature sets. This can come in handy when you troubleshoot AAA-related issues. Some of the commonly used show commands for TACACS+ and RADIUS are
show radius statistics
show caller user userid detail