Add test for pending events into the MessageEventModelTest

autotests/data/test-pending-sync.json

@@ -0,0 +1,22 @@
+{
+  "timeline": {
+    "events": [
+      {
+        "content": {
+          "body": "New plain message",
+          "msgtype": "m.text"
+        },
+        "event_id": "$pendingmerge:example.org",
+        "origin_server_ts": 123456,
+        "room_id":"#myroom:kde.org",
+        "sender":"@bob:kde.org",
+        "type":"m.room.message",
+        "unsigned": {
+          "transaction_id": "17017181543521"
+        }
+      }
+    ],
+    "limited": true,
+    "prev_batch": "t34-23535_0_0"
+  }
+}