Add support for file IO operations in the tester.
getFiles(path) -> get the list of file paths from a directory.
getDirectories(path) -> get the list of sub directories paths
from a directory.
readFile(path) -> read the content from a file.
writeFile(path, content) -> write the content to a file.
deleteFile(path) -> delete a file from the disk.
openFileDialog(startpath, filetypes, allowmultiselect) -> invoke an
open file dialog to select file(s).
saveFileDialog(defaultfilename, filetypes) -> invoke a save file dialog
to select file.