Add test for fs.copyFile

[YuechengWu]

There is currently no test for fs.copyFile().

I would like to create a test if the root directory does not exist and it should throw an error.
ex. fs.copyFile('\undefinedRootDirectoryFile', 'destination.txt', (err) => { ... }

Please if I could be assigned to work on this issue.

Thank you!

Yuecheng Wu