test_shutil contains a handy helper function called write_file(filename. contents). If *filename* is a tuple, os.path.join() is used to concatenate it to a path.

To be really useful, the resulting file name should be returned, so the user can work with it.

So instead of:
fn = os.path.join(x,y)
write_file(fn, 'contents')

I'd prefer:
fn = write_file((x,y), 'contents')

I have attached a simple patch that achieves this and also applied the resulting simplification to some of the tests.