Add more tests for rabinKarp.

Author: trekhleb

src/algorithms/string/rabin-karp/__test__/rabinKarp.test.js

@@ -11,6 +11,9 @@ describe('rabinKarp', () =>{
 });
 
 it('should find substring in a string',()=>{
+expect(rabinKarp('','')).toBe(0);
+expect(rabinKarp('a','')).toBe(0);
+expect(rabinKarp('a','a')).toBe(0);
 expect(rabinKarp('abcbcglx','abca')).toBe(-1);
 expect(rabinKarp('abcbcglx','bcgl')).toBe(3);
 expect(rabinKarp('abcxabcdabxabcdabcdabcy','abcdabcy')).toBe(15);