Use the endpoint mock to locally test your app logic fully. The mock gives you an abstraction of LayerZero messaging behavior and allows you to focus on your domain logic.
LayerZero assumes contracts on different chains whitelist the counterparts on the other chains. An N-chain UA would need to wire N^2 paths accurately. If the app has multiple configurations for each path, e.g. token swap, it will be even harder. The problem will compound if the UA needs to add new chains (worse if with different runtimes like EVM and Solana contracts).
It is very important for your configuration script unit-testable and portable to production.
After your deployment and configuration, you should do a quick smoke test to test whether message pathways are properly wired before shipping to production.
If you are doing everything right in the Testnet stage, Mainnet should just be repeating the process but with more caution. Good luck with the launch!