No Open Files
Confirm that all files that have been opened on this file system (with source, sink, and appendingSink) have since been closed. Call this in your test's
tearDown() function to confirm that your program hasn't leaked any open files.
Forgetting to close a file on a real file system is a severe error that may lead to a program crash. The operating system enforces a limit on how many files may be open simultaneously. On Linux this is getrlimit and is commonly adjusted with the
if any files are open when this function is called.