the symbol for the char array has the same name as the function and the string happens to have same values as assembly instructions of actual function. Basically you compile the program and treat it as the string, not quitr sure what the role of the UNNAMED is, but whatever,the core idea is that const valuse compile to object files that look for the computer indistinguishable from compiled code, it is all just ones and zeros.

Number of pairs will be half the total length of characters as two characters form one pair,
so in if total number of characters are odd then last pair will be pair[s.length()/2]

wtf indeed, if I had to guess it has to do with how assertions are made in the tester function used by tests, which seems to be in Preloaded section of kata, although the author will probably enlighten us