SERVER-14286 Additional tests for updates and findAndModifys that touch _id

Signed-off-by: Benety Goh <benety@mongodb.com>

jstests/core/update_find_and_modify_id.js

@@ -0,0 +1,44 @@
+// SERVER-4516 and SERVER-6913: test that update and findAndModify tolerate
+// an _id in the update document, as long as the _id will not be modified
+
+var t = db.jstests_server4516;
+var startingDoc = {_id: 1, a: 1};
+
+function prepare() {
+    t.drop();
+    t.save(startingDoc);
+}
+
+function update_succeeds(updateDoc, qid, resultDoc) {
+    prepare();
+    t.update({_id: qid}, updateDoc, true);
+    assert.eq(t.findOne({_id: qid}), resultDoc);
+
+    prepare();
+    t.findAndModify({query: {_id: qid}, update: updateDoc, upsert: true});
+    assert.eq(t.findOne({_id: qid}), resultDoc);
+}
+
+update_succeeds({_id: 1, a: 2}, 1, {_id: 1, a: 2});
+update_succeeds({$set: {_id: 1}}, 1, {_id: 1, a: 1});
+update_succeeds({_id: 1, b: "a"}, 1, {_id: 1, b: "a"});
+update_succeeds({_id: 2, a: 3}, 2, {_id: 2, a: 3});
+
+function update_fails(updateDoc, qid) {
+    prepare();
+    var res = t.update({_id: qid}, updateDoc, true);
+    assert.writeError(res);
+    assert.eq(t.count(), 1);
+    assert.eq(t.findOne(), startingDoc);
+
+    prepare();
+    assert.throws(function () {
+        t.findAndModify({query: {_id: qid}, update: updateDoc, upsert: true});
+    });
+    assert.eq(t.count(), 1);
+    assert.eq(t.findOne(), startingDoc);
+}
+
+update_fails({$set: {_id: 2}}, 1);
+update_fails({_id: 2, a: 3}, 1);
+update_fails({_id: 2, a: 3}, 3);