printf("\n  \e[32m\u2713 \e[90mok\e[0m\n\n");; 
after translation of c2rust:
printf(
        b"\n  \x1B[32m\xE2\x9C\x93 \x1B[90mok\x1B[0m\n\n\0" as *const u8
            as *const libc::c_char,
    ); 
Though both kind of string are supported by C, Rust only support the first unicode other than the second utf8, and compiler will report error as following:
print! ("\n  \x1B[32m\xE2\x9C\x93 \x1B[90mok\x1B[0m\n\n\0"); ^^^^ must be a character in the range [\x00-\x7f]