diff --git a/src/R3/Operators/AsObservable.cs b/src/R3/Operators/AsObservable.cs
index 1bfed5ce..abcac956 100644
--- a/src/R3/Operators/AsObservable.cs
+++ b/src/R3/Operators/AsObservable.cs
@@ -2,8 +2,6 @@
 
 public static partial class ObservableExtensions
 {
-    // TODO: test
-
     public static Observable<T> AsObservable<T>(this Observable<T> source)
     {
         if (source is AsObservable<T>) // already hide
diff --git a/src/R3/Operators/_Operators.cs b/src/R3/Operators/_Operators.cs
index ffaca00b..4d1732a3 100644
--- a/src/R3/Operators/_Operators.cs
+++ b/src/R3/Operators/_Operators.cs
@@ -20,7 +20,7 @@ public static partial class ObservableExtensions
     // Buffer + BUfferFrame => Chunk, ChunkFrame
 
     // Rx Merging:
-    //CombineLatest, Merge, Zip, WithLatestFrom, ZipLatest, Switch
+    // CombineLatest, Zip, WithLatestFrom, ZipLatest, Switch
 
     // Standard Query:
     // Distinct, DistinctBy, DistinctUntilChanged, Scan
diff --git a/tests/R3.Tests/OperatorTests/AsObservableTest.cs b/tests/R3.Tests/OperatorTests/AsObservableTest.cs
new file mode 100644
index 00000000..e160da49
--- /dev/null
+++ b/tests/R3.Tests/OperatorTests/AsObservableTest.cs
@@ -0,0 +1,74 @@
+namespace R3.Tests.OperatorTests;
+
+public class AsObservableTest
+{
+    [Fact]
+    public void AsObservable()
+    {
+        var p = new Subject<int>();
+
+        var l = p.AsObservable().AsObservable().ToLiveList();
+        p.OnNext(1);
+        p.OnNext(2);
+        p.OnNext(3);
+        p.OnCompleted();
+
+        l.AssertEqual([1, 2, 3]);
+        l.AssertIsCompleted();
+    }
+
+    [Fact]
+    public void AsIObservable()
+    {
+
+        {
+            var p = new Subject<int>();
+            var l = new List<int>();
+            Exception? ex = null;
+            bool completed = false;
+            p.AsIObservable().Subscribe(l.Add, e => ex = e, () => completed = true);
+
+            p.OnNext(1);
+            p.OnNext(2);
+            p.OnNext(3);
+            p.OnCompleted();
+
+            l.Should().Equal([1, 2, 3]);
+            completed.Should().BeTrue();
+        }
+        {
+            // error complete
+            var p = new Subject<int>();
+            var l = new List<int>();
+            Exception? ex = null;
+            bool completed = false;
+            p.AsIObservable().Subscribe(l.Add, e => ex = e, () => completed = true);
+
+            p.OnNext(1);
+            p.OnNext(2);
+            p.OnNext(3);
+            p.OnCompleted(new Exception("aaa"));
+
+            l.Should().Equal([1, 2, 3]);
+            ex!.Message.Should().Be("aaa");
+            completed.Should().BeFalse();
+        }
+        {
+            // error resume
+            var p = new Subject<int>();
+            var l = new List<int>();
+            Exception? ex = null;
+            bool completed = false;
+            p.AsIObservable().Subscribe(l.Add, e => ex = e, () => completed = true);
+
+            p.OnNext(1);
+            p.OnNext(2);
+            p.OnNext(3);
+            p.OnErrorResume(new Exception("bbb"));
+
+            l.Should().Equal([1, 2, 3]);
+            ex!.Message.Should().Be("bbb");
+            completed.Should().BeFalse();
+        }
+    }
+}
diff --git a/tests/R3.Tests/OperatorTests/OnErrorResumeAsFailureTest.cs b/tests/R3.Tests/OperatorTests/OnErrorResumeAsFailureTest.cs
new file mode 100644
index 00000000..f67e0503
--- /dev/null
+++ b/tests/R3.Tests/OperatorTests/OnErrorResumeAsFailureTest.cs
@@ -0,0 +1,21 @@
+namespace R3.Tests.OperatorTests;
+
+public class OnErrorResumeAsFailureTest
+{
+
+    [Fact]
+    public void OnErrorResumeAsFailure()
+    {
+        var subject = new Subject<int>();
+        var list = subject.OnErrorResumeAsFailure().ToLiveList();
+
+
+        subject.OnNext(10);
+        subject.OnErrorResume(new Exception("foo"));
+
+        list.AssertEqual([10]);
+        list.AssertIsCompleted();
+        list.CompletedValue.Exception!.Message.Should().Be("foo");
+
+    }
+}