Extract helper class TestFixtureHelper<TFixture>

src/EditorFeatures/TestUtilities/Completion/AbstractCompletionProviderTests.cs

@@ -38,8 +38,7 @@ public abstract class AbstractCompletionProviderTests<TWorkspaceFixture> : TestB
     {
         private static readonly TestComposition s_baseComposition = EditorTestCompositions.EditorFeatures.AddExcludedPartTypes(typeof(CompletionProvider));
 
-        private readonly object _workspaceFixtureGate = new();
-        private ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference _weakWorkspaceFixture;
+        private readonly TestFixtureHelper<TWorkspaceFixture> _fixtureHelper = new();
 
         protected readonly Mock<ICompletionSession> MockCompletionSession;
         private ExportProvider _lazyExportProvider;
@@ -56,17 +55,7 @@ protected virtual TestComposition GetComposition()
             => s_baseComposition.AddParts(GetCompletionProviderType());
 
         private protected ReferenceCountedDisposable<TWorkspaceFixture> GetOrCreateWorkspaceFixture()
-        {
-            lock (_workspaceFixtureGate)
-            {
-                if (_weakWorkspaceFixture.TryAddReference() is { } workspaceFixture)
-                    return workspaceFixture;
-
-                var result = new ReferenceCountedDisposable<TWorkspaceFixture>(new TWorkspaceFixture());
-                _weakWorkspaceFixture = new ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference(result);
-                return result;
-            }
-        }
+            => _fixtureHelper.GetOrCreateFixture();
 
         protected static async Task<bool> CanUseSpeculativeSemanticModelAsync(Document document, int position)
         {

src/EditorFeatures/TestUtilities/RefactoringHelpers/RefactoringHelpersTestBase.cs

@@ -22,21 +22,10 @@ namespace Microsoft.CodeAnalysis.Editor.UnitTests.RefactoringHelpers
     public abstract class RefactoringHelpersTestBase<TWorkspaceFixture> : TestBase
         where TWorkspaceFixture : TestWorkspaceFixture, new()
     {
-        private readonly object _workspaceFixtureGate = new();
-        private ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference _weakWorkspaceFixture;
+        private readonly TestFixtureHelper<TWorkspaceFixture> _fixtureHelper = new();
 
         private protected ReferenceCountedDisposable<TWorkspaceFixture> GetOrCreateWorkspaceFixture()
-        {
-            lock (_workspaceFixtureGate)
-            {
-                if (_weakWorkspaceFixture.TryAddReference() is { } workspaceFixture)
-                    return workspaceFixture;
-
-                var result = new ReferenceCountedDisposable<TWorkspaceFixture>(new TWorkspaceFixture());
-                _weakWorkspaceFixture = new ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference(result);
-                return result;
-            }
-        }
+            => _fixtureHelper.GetOrCreateFixture();
 
         protected Task TestAsync<TNode>(string text) where TNode : SyntaxNode => TestAsync<TNode>(text, Functions<TNode>.True);
 

src/EditorFeatures/TestUtilities/SignatureHelp/AbstractSignatureHelpProviderTests.cs

@@ -28,23 +28,12 @@ namespace Microsoft.CodeAnalysis.Editor.UnitTests.SignatureHelp
     public abstract class AbstractSignatureHelpProviderTests<TWorkspaceFixture> : TestBase
         where TWorkspaceFixture : TestWorkspaceFixture, new()
     {
-        private readonly object _workspaceFixtureGate = new();
-        private ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference _weakWorkspaceFixture;
+        private readonly TestFixtureHelper<TWorkspaceFixture> _fixtureHelper = new();
 
         internal abstract Type GetSignatureHelpProviderType();
 
         private protected ReferenceCountedDisposable<TWorkspaceFixture> GetOrCreateWorkspaceFixture()
-        {
-            lock (_workspaceFixtureGate)
-            {
-                if (_weakWorkspaceFixture.TryAddReference() is { } workspaceFixture)
-                    return workspaceFixture;
-
-                var result = new ReferenceCountedDisposable<TWorkspaceFixture>(new TWorkspaceFixture());
-                _weakWorkspaceFixture = new ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference(result);
-                return result;
-            }
-        }
+            => _fixtureHelper.GetOrCreateFixture();
 
         /// <summary>
         /// Verifies that sighelp comes up at the indicated location in markup ($$), with the indicated span [| ... |].

src/EditorFeatures/TestUtilities/TypeInferrer/TypeInferrerTestBase.cs

@@ -17,21 +17,10 @@ namespace Microsoft.CodeAnalysis.Editor.UnitTests.TypeInferrer
     public abstract class TypeInferrerTestBase<TWorkspaceFixture> : TestBase
         where TWorkspaceFixture : TestWorkspaceFixture, new()
     {
-        private readonly object _workspaceFixtureGate = new();
-        private ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference _weakWorkspaceFixture;
+        private readonly TestFixtureHelper<TWorkspaceFixture> _fixtureHelper = new();
 
         private protected ReferenceCountedDisposable<TWorkspaceFixture> GetOrCreateWorkspaceFixture()
-        {
-            lock (_workspaceFixtureGate)
-            {
-                if (_weakWorkspaceFixture.TryAddReference() is { } workspaceFixture)
-                    return workspaceFixture;
-
-                var result = new ReferenceCountedDisposable<TWorkspaceFixture>(new TWorkspaceFixture());
-                _weakWorkspaceFixture = new ReferenceCountedDisposable<TWorkspaceFixture>.WeakReference(result);
-                return result;
-            }
-        }
+            => _fixtureHelper.GetOrCreateFixture();
 
         private static async Task<bool> CanUseSpeculativeSemanticModelAsync(Document document, int position)
         {

src/EditorFeatures/TestUtilities/Utilities/TestFixtureHelper`1.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Roslyn.Utilities;
+
+namespace Microsoft.CodeAnalysis.Editor.UnitTests
+{
+    internal sealed class TestFixtureHelper<TFixture>
+        where TFixture : class, IDisposable, new()
+    {
+        private readonly object _gate = new();
+
+        /// <summary>
+        /// Holds a weak reference to the current test fixture instance. This reference allows
+        /// <see cref="GetOrCreateFixture"/> to access and add a reference to the current test fixture if one exists,
+        /// but does not prevent the fixture from being disposed after the last reference to it is released.
+        /// </summary>
+        private ReferenceCountedDisposable<TFixture>.WeakReference _weakFixture;
+
+        /// <summary>
+        /// Gets a reference to a test fixture, or creates it if one does not already exist.
+        /// </summary>
+        /// <remarks>
+        /// <para>The resulting test fixture will not be disposed until the last referencer disposes of its reference.
+        /// It is possible for more than one test fixture to be created during the life of any single test, but only one
+        /// test fixture will be live at any given point.</para>
+        ///
+        /// <para>The following shows how a block of test code can ensure a single test fixture is created and used
+        /// within any given block of code:</para>
+        ///
+        /// <code>
+        /// using (var fixture = GetOrCreateFixture())
+        /// {
+        ///   // The test fixture 'fixture' is guaranteed to not be released or replaced within this block
+        /// }
+        /// </code>
+        /// </remarks>
+        /// <returns>The test fixture instance.</returns>
+        internal ReferenceCountedDisposable<TFixture> GetOrCreateFixture()
+        {
+            lock (_gate)
+            {
+                if (_weakFixture.TryAddReference() is { } fixture)
+                    return fixture;
+
+                var result = new ReferenceCountedDisposable<TFixture>(new TFixture());
+                _weakFixture = new ReferenceCountedDisposable<TFixture>.WeakReference(result);
+                return result;
+            }
+        }
+    }
+}