update: test for throw, fix in TOC

TOC.md

@@ -1,6 +1,6 @@
-## Table of Contents
+# Table of Contents
 
-### Data Structures
+## Data Structures
 
 - [Singly Linked List](src/_DataStructures_/LinkedList)
 

src/_Problems_/compose-largest-number/compose-largest.test.js

@@ -1,4 +1,4 @@
-const { composeHighest, compare } = require('.');
+const { composeHighest, compare, ErrorMessage } = require('.');
 
 /**
  * Test cases
@@ -9,6 +9,10 @@ const { composeHighest, compare } = require('.');
 
 describe('Compose Largest Number', () => {
   describe('The main function returning the Highest NUmber', () => {
+    it('Should throw error for invalid argument', () => {
+      expect(() => composeHighest('abcd')).toThrow(ErrorMessage);
+    });
+
     it('Should return 9630 for `[3, 6, 0, 9]`', () => {
       expect(composeHighest([3, 6, 0, 9])).toEqual(9630);
     });

src/_Problems_/compose-largest-number/index.js

@@ -19,10 +19,12 @@ function compare(a, b) {
   return x > y ? -1 : 1;
 }
 
+const ErrorMessage = 'Invalid array/missing argument';
+
 /** final function */
 function composeHighest(arr) {
   if (!arr || !Array.isArray(arr)) {
-    throw new Error('Invalid array/missing argument');
+    throw new Error(ErrorMessage);
   }
 
   return Number(arr.sort(compare).join(''));
@@ -34,4 +36,4 @@ function composeHighest(arr) {
 // console.log(composeHighest([60, 548]) === 60548);
 // console.log(composeHighest([1, 34, 3, 98, 9, 76, 45, 4]) === 998764543431);
 
-module.exports = { composeHighest, compare };
+module.exports = { composeHighest, compare, ErrorMessage };