Implement test -N (file modified since last read)

[Mohamed-Moumni]

Description

The test -N test operator is currently unsupported it print the following output unsupported unary test op: -N, this command should return
file exists and has been modified since it was last read, and false otherwise.

Behavior

• Returns true if the file exist and mtime > atime (modified since last read)
• Returns false if the file doesn't exist
• Returns false if the file exist was read after its last modification.