fix(challenge): Stricter tests for "OOP: Constructor property"

* Also fixed an misleading sentence in the instruction.

Author: Greenheart

challenges/02-javascript-algorithms-and-data-structures/object-oriented-programming.json

@@ -407,12 +407,12 @@
       "description": [
         "There is a special <code>constructor</code> property located on the object instances <code>duck</code> and <code>beagle</code> that were created in the previous challenges:",
         "<blockquote>let duck = new Bird();<br>let beagle = new Dog();<br><br>console.log(duck.constructor === Bird);  //prints true<br>console.log(beagle.constructor === Dog);  //prints true</blockquote>",
-        "Note that the <code>constructor</code> property is the name of the constructor function that created the instance.",
+        "Note that the <code>constructor</code> property is a reference to the constructor function that created the instance.",
         "The advantage of the <code>constructor</code> property is that it's possible to check for this property to find out what kind of object it is. Here's an example of how this could be used:",
         "<blockquote>function joinBirdFraternity(candidate) {<br>&nbsp;&nbsp;if (candidate.constructor === Bird) {<br>&nbsp;&nbsp;&nbsp;&nbsp;return true;<br>&nbsp;&nbsp;} else {<br>&nbsp;&nbsp;&nbsp;&nbsp;return false;<br>&nbsp;&nbsp;}<br>}</blockquote>",
         "<strong>Note</strong><br>Since the <code>constructor</code> property can be overwritten (which will be covered in the next two challenges) it’s generally better to use the <code>instanceof</code> method to check the type of an object.",
         "<hr>",
-        "Write a <code>joinDogFraternity</code> function that takes a <code>candidate</code> parameter and returns <code>true</code> if the candidate is a <code>Dog</code> and returns <code>false</code> otherwise."
+        "Write a <code>joinDogFraternity</code> function that takes a <code>candidate</code> parameter and, using the <code>constructor</code> property, return <code>true</code> if the candidate is a <code>Dog</code>, otherwise return <code>false</code>."
       ],
       "challengeSeed": [
         "function Dog(name) {",
@@ -427,7 +427,8 @@
       ],
       "tests": [
         "assert(typeof(joinDogFraternity) === 'function', 'message: <code>joinDogFraternity</code> should be defined as a function.');",
-        "assert(joinDogFraternity(new Dog(\"\")) === true, 'message: <code>joinDogFraternity</code> should return true if<code>candidate</code> is an instance of <code>Dog</code>.');"
+        "assert(joinDogFraternity(new Dog(\"\")) === true, 'message: <code>joinDogFraternity</code> should return true if<code>candidate</code> is an instance of <code>Dog</code>.');",
+        "assert(/\\.constructor/.test(code) && !/instanceof/.test(code), 'message: <code>joinDogFraternity</code> should use the <code>constructor</code> property.');"
       ],
       "solutions": [],
       "hints": [],