site_dir, or vendor_dir, is the location where the default version of bundler & rubygems gets installed. These folders are placed directly in the LOAD_PATH, so they cannot hold any nested gem directory structure. So a single copy of either rubygems or bundler can be placed in these folders.
What the tests are actually testing is the TODO comment that I'm removing: that installing the default copy of bundler doesn't affect any already installed copies of bundler as regular gems.
Added by deivid (David RodrÃguez) over 5 years ago
[rubygems/rubygems] Remove misleading comments
site_dir, orvendor_dir, is the location where the default versionof bundler & rubygems gets installed. These folders are placed directly
in the LOAD_PATH, so they cannot hold any nested gem directory
structure. So a single copy of either rubygems or bundler can be placed
in these folders.
What the tests are actually testing is the TODO comment that I'm
removing: that installing the default copy of bundler doesn't affect any
already installed copies of bundler as regular gems.
https://github.com/rubygems/rubygems/commit/7ca8831d72