fixed UndoManager tests

Tests/YSwiftTests/YUndoManagerTests.swift

@@ -92,21 +92,22 @@ class YUndoManagerTests: XCTestCase {
         let localOrigin = Origin("local")
 
         let remoteDocument = YDocument()
-        let remoteText = document.getOrCreateText(named: "test")
+        let remoteText = remoteDocument.getOrCreateText(named: "test")
         manager.addOrigin(localOrigin) // only track transaction from local origin
 
         // create some changes locally
         document.transactSync(origin: localOrigin) { txn in
             self.text.insert("hello", at: 0, in: txn)
-            self.manager.wrap() // add changes on a stack: they will be undone as one
         }
+        self.manager.wrap() // add changes on a stack: they will be undone as one
 
         exchangeUpdates(document, remoteDocument)
 
         // concurrent change on the remote replica
         document.transactSync(origin: localOrigin) { txn in
             self.text.insert(" world", at: 5, in: txn)
         }
+        self.manager.wrap() // add next batch of changes on a stack
         remoteText.insert("<break>", at: 1)
 
         XCTAssertEqual(text.getString(), "hello world")