Here is a system usage command in mac terminal. fs_usage can show you all file system action, I use it for asset-pipeline debugging.
When I need check if an asset file is currently loaded, I’ll use it like
$ sudo fs_usage | grep FILE_NAME.js
It also can be used for checking how the precompilation process works. Once I used it to find a process issue of recursive compilation in the requirejs-rails gem, and reduced compilation time by 95%.