Update: Fix the f_directory unit tests and finish writing them.

Update: Fix the f_directory unit tests and finish writing them.

The problem with the unit tests not being run (especially on Github) appears to be the result of compiler optimizations.
Fix this by disabling compiler optimizations in the mock functions and add appropriate commetns explaining this.

Do not wrap/mock strncmp() and strnlen().

The directory tests are now completed.