fix(book/hashmap): exercise example and add tests

Author: amejiarosario

book/content/part02/hash-map.asc

@@ -486,7 +486,7 @@ function longestSubstring(s) {
 .Examples
 [source, javascript]
 ----
-longestSubstring('abcdaefg'); // 4 ('abcd' or 'aefg')
+longestSubstring('abcdaefg'); // 7 ('bcdaefg')
 longestSubstring('abbaa'); // 2 ('ab')
 longestSubstring('abbadvdf') // 4 ('badv')
 ----

book/interview-questions/longest-substring-without-repeating-characters.spec.js

@@ -20,5 +20,11 @@ const { lenLongestSubstring } = require('./longest-substring-without-repeating-c
       const expected = 5;
       expect(fn(actual)).toEqual(expected);
     });
+
+    it('should work with example', () => {
+      const actual = 'abcdaefg';
+      const expected = 7;
+      expect(fn(actual)).toEqual(expected);
+    });
   });
 });