[easy_train] Things may break if required executables are found through local directory instead of PATH

[Sopel97]

We sometimes call executables with different cwd so they may not be found if they were originally only found in the same directory as the script. (someone actually had gcc in the same directory as the script...). What would be a good cwd to use for verification?

[vondele]

tempfile.mkdtemp() ?