Tested that an error is thrown when we try to change a document's _id

test/db.test.js

@@ -614,6 +614,23 @@ describe('Database', function () {
       });
     });
 
+    it('Cant change the _id of a document', function (done) {
+      d.insert({ a: 2 }, function (err, newDoc) {
+        d.update({ a: 2 }, { _id: 'nope' }, {}, function (err) {
+          assert.isDefined(err);
+
+          d.find({}, function (err, docs) {
+            docs.length.should.equal(1);
+            Object.keys(docs[0]).length.should.equal(2);
+            docs[0].a.should.equal(2);
+            docs[0]._id.should.equal(newDoc._id);
+
+            done();
+          });
+        });
+      });
+    });
+
   });   // ==== End of 'Update' ==== //