"" <=> "" == 0
"a" <=> "a" == 0
"aa" <=> "aaa" == -1
"aaa" <=> "aa" == 1
"a" <=> "b" == -1
"b" <=> "a" == 1
"" <=> "b" == -1
"c" <=> "" == 1
"abc" <=> "cba" == 1
"cabc" <=> "cxc" == 0
"zy" <=> "abw" == 0
"abab" <=> "xx" == 0
"abab" <=> "ww" == -1
"w" <=> "z" == 1
"xcy" <=> "zw" == -1