Add UndoManagerRegistration Tests

Author: thecoolwinter

CodeEditTests/Features/Editor/UndoManagerRegistrationTests.swift

@@ -0,0 +1,35 @@
+//
+//  UndoManagerRegistrationTests.swift
+//  CodeEditTests
+//
+//  Created by Khan Winter on 7/3/25.
+//
+
+@testable import CodeEdit
+import Testing
+import Foundation
+import CodeEditTextView
+
+@Suite
+struct UndoManagerRegistrationTests {
+    let registrar = UndoManagerRegistration()
+    let file = CEWorkspaceFile(url: URL(filePath: "/fake/dir/file.txt"))
+    let textView = TextView(string: "hello world")
+
+    @Test
+    func newUndoManager() {
+        let manager = registrar.manager(forFile: file)
+        #expect(manager.canUndo == false)
+    }
+
+    @Test
+    func undoManagersRetained() throws {
+        let manager = registrar.manager(forFile: file)
+        textView.setUndoManager(manager)
+        manager.registerMutation(.init(insert: "hello", at: 0, limit: 11))
+
+        let sameManager = registrar.manager(forFile: file)
+        #expect(manager === sameManager)
+        #expect(sameManager.canUndo)
+    }
+}