add find-2nd-max tests

Author: deadem

src/_Problems_/find-2nd-max/index.js

@@ -20,3 +20,7 @@ function findSecondMax(arr) {
   }
   return max2;
 }
+
+module.exports = {
+  findSecondMax,
+};

src/_Problems_/find-2nd-max/index.test.js

@@ -0,0 +1,15 @@
+const { findSecondMax } = require('.');
+
+describe('FindSecondMax', () => {
+  it('Should return 6', () => {
+    expect(findSecondMax([9, 2, 3, 6])).toEqual(6);
+  });
+
+  it('Should return -1', () => {
+    expect(findSecondMax([0, -1, -2, 0])).toEqual(-1);
+  });
+
+  it('Should return 0', () => {
+    expect(findSecondMax([-2, -1, 0, 1])).toEqual(0);
+  });
+});