Added tests to ensure constructor is properly applied to subtypes

lib/class.js

@@ -175,6 +175,9 @@ var extend = ( function( extending )
                 // call the constructor, if one was provided
                 if ( this.__construct instanceof Function )
                 {
+                    // note that since 'this' refers to the new class (even
+                    // subtypes), and since we're using apply with 'this', the
+                    // constructor will be applied to subtypes without a problem
                     this.__construct.apply( this, arguments );
                 }
             };

test/test-class-constructor.js

@@ -94,3 +94,36 @@ for ( var i = 0, len = args.length; i < len; i++ )
         "Arguments should be passed to the constructor: " + i
     );
 }
+
+var SubFoo = Foo.extend(
+{
+    args: [ 'should', 'be', 'overwritten' ],
+} );
+
+construct_count   = 0;
+construct_context = null;
+
+var args2  = [ 'fried', 'pickle' ],
+    subobj = new SubFoo( args2[ 0 ], args2[ 1 ] );
+
+assert.equal(
+    construct_count,
+    1,
+    "Parent constructor should be called for subtype if not overridden"
+);
+
+assert.equal(
+    construct_context,
+    subobj,
+    "Parent constructor is run in context of the subtype"
+);
+
+// this should be implied by the previous test, but let's add it for some peace
+// of mind
+assert.ok(
+    ( ( subobj.args[ 0 ] === args2[ 0 ] )
+        && ( subobj.args[ 1 ] == args2[ 1 ] )
+    ),
+    "Parent constructor sets values on subtype"
+);
+