fix: Clarify mutate array with const challenge (#15745)

Instructions for Mutate an Array Declared with const was unclear and
included unnecessary learning materials. This commit aims to clarify the
instructions for what the challenge requires, and also add in missing
challenge tests.

Closes #14832

challenges/02-javascript-algorithms-and-data-structures/es6.json

@@ -138,29 +138,30 @@
       "id": "587d7b87367417b2b2512b42",
       "title": "Mutate an Array Declared with const",
       "description": [
-        "The <code>const</code> declaration has many use-cases in modern JavaScript.",
+        "The <code>const</code> declaration has many use cases in modern JavaScript.",
         "Some developers prefer to assign all their variables using <code>const</code> by default, unless they know they will need to reassign the value. Only in that case, they use <code>let</code>.",
         "However, it is important to understand that objects (including arrays and functions) assigned to a variable using <code>const</code> are still mutable. Using the <code>const</code> declaration only prevents reassignment of the variable identifier.",
-        "<blockquote>\"use strict\";<br>const s = [5, 6, 7];<br>s = [1, 2, 3]; // throws error, trying to assign a const<br>s[7] = 45; // works just as it would with an array declared with var</blockquote>",
+        "<blockquote>\"use strict\";<br>const s = [5, 6, 7];<br>s = [1, 2, 3]; // throws error, trying to assign a const<br>s[2] = 45; // works just as it would with an array declared with var or let<br>console.log(s); // returns [5, 6, 45]</blockquote>",
-        "As you can see, you can mutate the object (<code>[5, 6, 7]</code>) itself and the variable identifier (<code>s</code>) will still point to the altered array. Like all arrays, the array assigned to <code>s</code> is mutable, but because <code>const</code> was used, you cannot use the variable identifier, <code>s</code>, to point to a different array using the assignment operator.",
+        "As you can see, you can mutate the object <code>[5, 6, 7]</code> itself and the variable <code>s</code> will still point to the altered array <code>[5, 6, 45]</code>. Like all arrays, the array elements in <code>s</code> are mutable, but because <code>const</code> was used, you cannot use the variable identifier <code>s</code> to point to a different array using the assignment operator.",
-        "To make an object immutable, you can use <code>Object.freeze()</code>.",
         "<hr>",
-        "An array is declared as <code>const s = [5, 7, 2]</code>. Change the array to <code>[2, 5, 7]</code>.",
+        "An array is declared as <code>const s = [5, 7, 2]</code>. Change the array to <code>[2, 5, 7]</code> using various element assignment.",
         "<strong>Note</strong><br>Don't forget to add <code>\"use strict\";</code> to the top of your code."
       ],
       "challengeSeed": [
-        "const s = [ 5, 7, 2 ];",
+        "const s = [5, 7, 2];",
         "// change code below this line",
+        "",
         "s = [2, 5, 7];",
+        "",
         "// change code above this line",
         "// Test your code",
         "console.log(s);"
       ],
       "tests": [
-        "// Test user did not replace const keyword",
+        "assert(code.match(/const/g), 'message: Do not replace <code>const</code> keyword.');",
-        "// Test s is const",
+        "assert(code.match(/const\\s+s/g), 'message: <code>s</code> is declared with <code>const</code>.');",
-        "assert.deepEqual(s, [2, 5, 7], 'message: <code>s</code> should be equal to <code>[2, 5, 7]</code>.');",
+        "assert(code.match(/const\\s+s\\s*?=\\s*?\\[\\s*?2\\s*?,\\s*?5\\s*?,\\s*?7\\s*?\\]\\s*?;/g), 'message: Do not change the original array declaration.');",
-        "assert(!Object.isFrozen(s), 'message: <code>s</code> should not be frozen.');"
+        "assert.deepEqual(s, [2, 5, 7], 'message: <code>s</code> should be equal to <code>[2, 5, 7]</code>.');"
       ],
       "type": "waypoint",
       "releasedOn": "Feb 17, 2017",