text: const strStr = require("./index");
  
  test("found substring returns first element index", () => {
    expect(strStr("hello", "ll")).toEqual(2);
  });
  
  test("empty substring returns 0", () => {
    expect(strStr("hello", "")).toEqual(0);
  });
  
  test("no found substring returns -1", () => {
    expect(strStr("hello", "mandi")).toEqual(-1);
  });
  