Added a test on modification of upserted document

test/db.test.js

@@ -915,12 +915,19 @@ describe('Database', function () {
               docs.length.should.equal(1);   // Default option for upsert is false
               docs[0].something.should.equal("created ok");
               
+              // Modifying the returned upserted document doesn't modify the database
+              newDoc.newField = true;
+              d.find({}, function (err, docs) {
+                docs[0].something.should.equal("created ok");
+                assert.isUndefined(docs[0].newField);
+              
                 done();
               });
             });
           });
         });
       });
+    });
 
     it('Cannot perform update if the update query is not either registered-modifiers-only or copy-only, or contain badly formatted fields', function (done) {
       d.insert({ something: 'yup' }, function () {