test: add test for tas oper and fix issue

BallanceTasEditor/BallanceTasEditorTests/TasSequenceUtils.cs

@@ -0,0 +1,22 @@
+using BallanceTasEditor.Backend;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BallanceTasEditorTests {
+
+    internal static class TasSequenceUtils {
+
+        internal static IEnumerable<ITasSequence> EnumerateTasSequenceImplementation() {
+            yield return new ListTasSequence();
+            yield return new LegacyTasSequence();
+            // TODO: Add GapBufferTasSequence once we finish it.
+            //yield return new GapBufferTasSequence();
+        }
+
+    }
+
+}