on Mac OS X mdm.FileSystem.fileExists and mdm.FileSystem.folderExists due to underlying implementation are effectively working in the same way and can be used with both files and folders.
For example mdm.FileSystem.fileExists(...) method can be used to check folders and files. The same is supported by mdm.FileSystem.folderExists.
That is different from Windows implementation that will always return "false" for checks for folders with mdm.FileSystem.fileExists and for checks of file path with mdm.FileSystem.folderExists.

The provided example checks if application path and application filename path exists using mdm.FileSystem.fileExists and mdm.FileSystem.folderExists respectively.
Both checks returns true (positive) on Mac OS X while expected results are false (as on Windows).

This leaves developers without way of checking if given path is folder or file (not yet introduced feature in api). This could be work around on Mac OS X with use of AppleScript similar to below one:

set DOES_NOT_EXITS to "does not exists"
set results to "$HFS_OR_POSIX_PATH"
try
tell application "System Events" to get class of item (results as text)
on error
set results to DOES_NOT_EXITS
end try


To repeat issue compile provided sample from "output" folder and then run on your machine.
Expected results are "false" while current implementation returns true