Added some ExpressionObserver lifetime tests.

src/Markup/Perspex.Markup/Data/ExpressionObserver.cs

@@ -156,6 +156,11 @@ namespace Perspex.Markup.Data
         /// <inheritdoc/>
         string IDescription.Description => Expression;
 
+        /// <summary>
+        /// Gets the root expression node. Used for testing.
+        /// </summary>
+        internal ExpressionNode Node => _node;
+
         /// <summary>
         /// Gets the leaf node.
         /// </summary>

tests/Perspex.Markup.UnitTests/Data/ExpressionObserverTests_Lifetime.cs

@@ -0,0 +1,70 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Reactive;
+using System.Reactive.Subjects;
+using Microsoft.Reactive.Testing;
+using Perspex.Markup.Data;
+using Xunit;
+
+namespace Perspex.Markup.UnitTests.Data
+{
+    public class ExpressionObserverTests_Lifetime
+    {
+        [Fact(Skip = "Not working yet")]
+        public void Should_Complete_When_Source_Observable_Completes()
+        {
+            var source = new BehaviorSubject<object>(1);
+            var target = new ExpressionObserver(source, "Foo");
+            var completed = false;
+
+            target.Subscribe(_ => { }, () => completed = true);
+            source.OnCompleted();
+
+            Assert.True(completed);
+        }
+
+        [Fact]
+        public void Should_Unsubscribe_From_Source_Observable()
+        {
+            var scheduler = new TestScheduler();
+            var source = scheduler.CreateColdObservable(
+                OnNext(1, new { Foo = "foo" }));
+            var target = new ExpressionObserver(source, "Foo");
+            var result = new List<object>();
+
+            using (target.Subscribe(x => result.Add(x)))
+            using (target.Subscribe(_ => { }))
+            {
+                scheduler.Start();
+            }
+
+            Assert.Equal(new[] { PerspexProperty.UnsetValue, "foo" }, result);
+            Assert.Equal(1, source.Subscriptions.Count);
+            Assert.NotEqual(Subscription.Infinite, source.Subscriptions[0].Unsubscribe);
+        }
+
+        [Fact]
+        public void Should_Set_Node_Target_To_Null_On_Unsubscribe()
+        {
+            var target = new ExpressionObserver(new { Foo = "foo" }, "Foo");
+            var result = new List<object>();
+
+            using (target.Subscribe(x => result.Add(x)))
+            using (target.Subscribe(_ => { }))
+            {
+                Assert.NotNull(target.Node.Target);
+            }
+
+            Assert.Equal(new[] { "foo" }, result);
+            Assert.Null(target.Node.Target);
+        }
+
+        private Recorded<Notification<object>> OnNext(long time, object value)
+        {
+            return new Recorded<Notification<object>>(time, Notification.CreateOnNext<object>(value));
+        }
+    }
+}

tests/Perspex.Markup.UnitTests/Data/ExpressionObserverTests_Property.cs

@@ -355,7 +355,7 @@ namespace Perspex.Markup.UnitTests.Data
         {
         }
 
-        public Recorded<Notification<object>> OnNext(long time, object value)
+        private Recorded<Notification<object>> OnNext(long time, object value)
         {
             return new Recorded<Notification<object>>(time, Notification.CreateOnNext<object>(value));
         }

tests/Perspex.Markup.UnitTests/Perspex.Markup.UnitTests.csproj

@@ -84,6 +84,7 @@
     <Compile Include="ControlLocatorTests.cs" />
     <Compile Include="Data\ExpressionNodeBuilderTests.cs" />
     <Compile Include="Data\ExpressionNodeBuilderTests_Errors.cs" />
+    <Compile Include="Data\ExpressionObserverTests.cs" />
     <Compile Include="Data\ExpressionObserverTests_Indexer.cs" />
     <Compile Include="Data\ExpressionObserverTests_Negation.cs" />
     <Compile Include="Data\ExpressionObserverTests_Observable.cs" />