fails:Kernel#open opens a file when called with a block
fails:Kernel#open sets permissions of newly created file
fails:Kernel#open sets the file as writable if perm is nil
fails:Kernel#open allows nil for perm
fails:Kernel#open allows Integer-like objects for perm
fails:Kernel#open calls #to_open on argument
fails:Kernel#open raises a TypeError if passed a non-String that does not respond to #to_open
