diff --git a/UaClient.UnitTests/UnitTests/ServiceExtensionsTests.cs b/UaClient.UnitTests/UnitTests/ServiceExtensionsTests.cs
new file mode 100644
index 0000000..797b9fc
--- /dev/null
+++ b/UaClient.UnitTests/UnitTests/ServiceExtensionsTests.cs
@@ -0,0 +1,187 @@
+using FluentAssertions;
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Workstation.ServiceModel.Ua;
+using Xunit;
+
+namespace Workstation.UaClient.UnitTests
+{
+    public class ServiceExtensionsTests
+    {
+        private static Task Never() => Task.Delay(-1);
+
+        private static async Task<T> Never<T>(T value)
+        {
+            await Never();
+            return value;
+        }
+
+        [Fact]
+        public void ToVariantArray()
+        {
+            var input = new object[] { 1, 2, 3, 70 };
+            var expected = new Variant[] { 1, 2, 3, 70 };
+
+            input.ToVariantArray()
+                .Should().BeEquivalentTo(expected);
+        }
+        
+        [Fact]
+        public void ToVariantArrayEmpty()
+        {
+            var input = new object[] { };
+            var expected = new Variant[] { };
+
+            input.ToVariantArray()
+                .Should().BeEquivalentTo(expected);
+        }
+        
+        [Fact]
+        public void ToVariantArrayNull()
+        {
+            var input = default(object[]);
+
+            input.Invoking(i => i.ToVariantArray())
+                .Should().Throw<ArgumentNullException>();
+        }
+        
+        [Fact]
+        public void ToObjectArray()
+        {
+            var input = new Variant[] { 1, 2, 3, 70 };
+            var expected = new object[] { 1, 2, 3, 70 };
+
+            input.ToObjectArray()
+                .Should().BeEquivalentTo(expected);
+        }
+        
+        [Fact]
+        public void ToObjectArrayEmpty()
+        {
+            var input = new Variant[] { };
+            var expected = new object[] { };
+
+            input.ToObjectArray()
+                .Should().BeEquivalentTo(expected);
+        }
+        
+        [Fact]
+        public void ToObjectArrayNull()
+        {
+            var input = default(Variant[]);
+
+            input.Invoking(i => i.ToObjectArray())
+                .Should().Throw<ArgumentNullException>();
+        }
+
+        [Fact]
+        public void WithCancellationCompleted()
+        {
+            var task = Task.CompletedTask;
+
+            task.WithCancellation(default).IsCompleted
+                .Should().BeTrue();
+        }
+        
+        [Fact]
+        public async Task WithCancellationFastTask()
+        {
+            using (var tcs = new CancellationTokenSource())
+            {
+                var fast = Task.Delay(1);
+                var task = fast.WithCancellation(tcs.Token);
+
+                await task.Invoking(t => t)
+                    .Should().NotThrowAsync();
+            }
+        }
+
+        [Fact]
+        public async Task WithCancellation()
+        {
+            using (var tcs = new CancellationTokenSource())
+            {
+                var never = Never();
+                var task = never.WithCancellation(tcs.Token);
+                tcs.Cancel();
+
+                await task.Invoking(t => t)
+                    .Should().ThrowAsync<OperationCanceledException>();
+            }
+        }
+        
+        [Fact]
+        public void ValueWithCancellationCompleted()
+        {
+            var task = Task.FromResult(10);
+
+            task.WithCancellation(default).IsCompleted
+                .Should().BeTrue();
+        }
+
+        [Fact]
+        public async Task ValueWithCancellation()
+        {
+            using (var tcs = new CancellationTokenSource())
+            {
+                var never = Never(10);
+                var task = never.WithCancellation(tcs.Token);
+                tcs.Cancel();
+
+                await task.Invoking(t => t)
+                    .Should().ThrowAsync<OperationCanceledException>();
+            }
+        }
+        
+        [Fact]
+        public void WithTimeoutAfterCompleted()
+        {
+            var task = Task.CompletedTask;
+
+            task.WithTimeoutAfter(-1).IsCompleted
+                .Should().BeTrue();
+        }
+        
+        [Fact]
+        public async Task WithTimeoutAfterFastTask()
+        {
+            var fast = Task.Delay(1);
+            var task = fast.WithTimeoutAfter(-1);
+
+            await task.Invoking(t => t)
+                .Should().NotThrowAsync();
+        }
+
+        [Fact]
+        public async Task WithTimeoutAfter()
+        {
+            var never = Never();
+            var task = never.WithTimeoutAfter(0);
+
+            await task.Invoking(t => t)
+                .Should().ThrowAsync<TimeoutException>();
+        }
+        
+        [Fact]
+        public void ValueWithTimeoutAfterCompleted()
+        {
+            var task = Task.FromResult(10);
+
+            task.WithTimeoutAfter(-1).IsCompleted
+                .Should().BeTrue();
+        }
+
+        [Fact]
+        public async Task ValueWithTimeoutAfter()
+        {
+            var never = Never(10);
+            var task = never.WithTimeoutAfter(0);
+
+            await task.Invoking(t => t)
+                .Should().ThrowAsync<TimeoutException>();
+        }
+    }
+}
diff --git a/UaClient.UnitTests/UnitTests/ServiceSetTests.cs b/UaClient.UnitTests/UnitTests/ServiceSetTests.cs
index e7dd509..bd8fc04 100644
--- a/UaClient.UnitTests/UnitTests/ServiceSetTests.cs
+++ b/UaClient.UnitTests/UnitTests/ServiceSetTests.cs
@@ -730,5 +730,138 @@ public async Task UnregisterNodesAsync()
             channel.Request
                 .Should().BeSameAs(request);
         }
+
+        /*
+         * ServiceExtensions
+         * Tests for: ServiceExtensions.css
+         */
+        [Fact]
+        public async Task ConditionRefreshAsync()
+        {
+            var response = new CallResponse
+            {
+                Results = new CallMethodResult[]
+                {
+                    new CallMethodResult
+                    {
+                        StatusCode = StatusCodes.BadAttributeIdInvalid
+                    }
+                }
+            };
+            var channel = new TestRequestChannel(response);
+
+            var ret = await channel.ConditionRefreshAsync(subscriptionId: 100);
+
+            ret
+                .Should().Be((StatusCode)StatusCodes.BadAttributeIdInvalid);
+
+            channel.Request
+                .Should().BeEquivalentTo(new
+                {
+                    MethodsToCall = new[]
+                    {
+                        new
+                        {
+                            ObjectId = NodeId.Parse(ObjectTypeIds.ConditionType),
+                            MethodId = NodeId.Parse(MethodIds.ConditionType_ConditionRefresh),
+                            InputArguments = new Variant[] { 100u }
+                        }
+                    }
+                });
+        }
+
+        [Fact]
+        public async Task AcknowledgeAsync()
+        {
+            var condition = new AcknowledgeableCondition();
+            var comment = new LocalizedText("Comment");
+            var response = new CallResponse
+            {
+                Results = new CallMethodResult[]
+                {
+                    new CallMethodResult
+                    {
+                        StatusCode = StatusCodes.BadAttributeIdInvalid
+                    }
+                }
+            };
+            var channel = new TestRequestChannel(response);
+
+            var ret = await channel.AcknowledgeAsync(condition, comment);
+
+            ret
+                .Should().Be((StatusCode)StatusCodes.BadAttributeIdInvalid);
+
+            channel.Request
+                .Should().BeEquivalentTo(new
+                {
+                    MethodsToCall = new[]
+                    {
+                        new
+                        {
+                            ObjectId = condition.ConditionId,
+                            MethodId = NodeId.Parse(MethodIds.AcknowledgeableConditionType_Acknowledge),
+                            InputArguments = new Variant[] { condition.EventId, comment }
+                        }
+                    }
+                });
+        }
+        
+        [Fact]
+        public void AcknowledgeAsyncNull()
+        {
+            var response = new CallResponse();
+            var channel = new TestRequestChannel(response);
+
+            channel.Invoking(c => c.AcknowledgeAsync(null, "Comment"))
+                .Should().Throw<ArgumentNullException>();
+        }
+
+        [Fact]
+        public async Task ConfirmAsync()
+        {
+            var condition = new AcknowledgeableCondition();
+            var comment = new LocalizedText("Comment");
+            var response = new CallResponse
+            {
+                Results = new CallMethodResult[]
+                {
+                    new CallMethodResult
+                    {
+                        StatusCode = StatusCodes.BadAttributeIdInvalid
+                    }
+                }
+            };
+            var channel = new TestRequestChannel(response);
+
+            var ret = await channel.ConfirmAsync(condition, comment);
+
+            ret
+                .Should().Be((StatusCode)StatusCodes.BadAttributeIdInvalid);
+
+            channel.Request
+                .Should().BeEquivalentTo(new
+                {
+                    MethodsToCall = new[]
+                    {
+                        new
+                        {
+                            ObjectId = condition.ConditionId,
+                            MethodId = NodeId.Parse(MethodIds.AcknowledgeableConditionType_Confirm),
+                            InputArguments = new Variant[] { condition.EventId, comment }
+                        }
+                    }
+                });
+        }
+        
+        [Fact]
+        public void ConfirmAsyncNull()
+        {
+            var response = new CallResponse();
+            var channel = new TestRequestChannel(response);
+
+            channel.Invoking(c => c.ConfirmAsync(null, "Comment"))
+                .Should().Throw<ArgumentNullException>();
+        }
     }
 }
diff --git a/UaClient/ServiceModel/Ua/StatusCode.cs b/UaClient/ServiceModel/Ua/StatusCode.cs
index 8951449..d139d74 100644
--- a/UaClient/ServiceModel/Ua/StatusCode.cs
+++ b/UaClient/ServiceModel/Ua/StatusCode.cs
@@ -3,7 +3,7 @@
 
 namespace Workstation.ServiceModel.Ua
 {
-    public struct StatusCode
+    public readonly struct StatusCode
     {
         private const uint SeverityMask = 0xC0000000u;
         private const uint SeverityGood = 0x00000000u;
diff --git a/UaClient/ServiceModel/Ua/Variant.cs b/UaClient/ServiceModel/Ua/Variant.cs
index f84b88f..ab1483e 100644
--- a/UaClient/ServiceModel/Ua/Variant.cs
+++ b/UaClient/ServiceModel/Ua/Variant.cs
@@ -40,7 +40,7 @@ public enum VariantType
         DiagnosticInfo = 25,
     }
 
-    public struct Variant
+    public readonly struct Variant
     {
         public static readonly Variant Null = default(Variant);