fails:File.dirname returns all the components of filename except the last one
fails:File.dirname returns a String
fails:File.dirname does not modify its argument
fails:File.dirname ignores a trailing /
fails:File.dirname returns the return all the components of filename except the last one (unix format)
fails:File.dirname returns all the components of filename except the last one (edge cases on all platforms)
fails:File.dirname returns all the components of filename except the last one (edge cases on non-windows)
fails:File.dirname accepts an object that has a #to_path method
fails:File.dirname raises a TypeError if not passed a String type
