Adding a simple test for executable files

[Ptipiak]

resolve #1106 close #1106

[Ptipiak]

The nix package offer function to change a file chmod, but I though this simple test could do the job.
The test make sure the file with chmod 005 doesn't appear in the result set.
Let me know if it's enough or if it would be better to actually make two assertion to test if the file appear/disappear from the result set after it's chmod as been changed.