diff --git a/X10D.Tests/X10D.Tests.csproj b/X10D.Tests/X10D.Tests.csproj
index 00ea605..aa5bbd2 100644
--- a/X10D.Tests/X10D.Tests.csproj
+++ b/X10D.Tests/X10D.Tests.csproj
@@ -17,7 +17,7 @@
     <ItemGroup>
         <PackageReference Include="Microsoft.Extensions.Hosting" Version="7.0.1"/>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.5.0"/>
-        <PackageReference Include="Moq" Version="4.18.4"/>
+        <PackageReference Include="NSubstitute" Version="5.0.0"/>
         <PackageReference Include="NUnit" Version="3.13.3"/>
         <PackageReference Include="NUnit3TestAdapter" Version="4.4.2"/>
         <PackageReference Include="NUnit.Analyzers" Version="3.6.1"/>
diff --git a/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAll.cs b/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAll.cs
index ebce1e4..3330de8 100644
--- a/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAll.cs
+++ b/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAll.cs
@@ -1,5 +1,5 @@
 using System.Collections.ObjectModel;
-using Moq;
+using NSubstitute;
 using NUnit.Framework;
 using X10D.Collections;
 
@@ -13,16 +13,17 @@ public partial class CollectionTests
         [Test]
         public void ClearAndDisposeAll_ShouldClearAndDisposeAllItems_WhenCalledWithValidList()
         {
-            var mock1 = new Mock<IDisposable>();
-            var mock2 = new Mock<IDisposable>();
-            var mock3 = new Mock<IDisposable>();
-            var list = new List<IDisposable> {mock1.Object, mock2.Object, mock3.Object};
+            var substitute1 = Substitute.For<IDisposable>();
+            var substitute2 = Substitute.For<IDisposable>();
+            var substitute3 = Substitute.For<IDisposable>();
+            var list = new List<IDisposable> {substitute1, substitute2, substitute3};
 
             list.ClearAndDisposeAll();
 
-            mock1.Verify(i => i.Dispose(), Times.Once);
-            mock2.Verify(i => i.Dispose(), Times.Once);
-            mock3.Verify(i => i.Dispose(), Times.Once);
+            substitute1.Received(1).Dispose();
+            substitute2.Received(1).Dispose();
+            substitute3.Received(1).Dispose();
+
             Assert.That(list, Is.Empty);
         }
 
@@ -36,8 +37,8 @@ public partial class CollectionTests
         [Test]
         public void ClearAndDisposeAll_ShouldThrowInvalidOperationException_WhenCalledWithReadOnlyList()
         {
-            var mock = new Mock<IDisposable>();
-            var list = new ReadOnlyCollection<IDisposable>(new List<IDisposable> {mock.Object});
+            var substitute = Substitute.For<IDisposable>();
+            var list = new ReadOnlyCollection<IDisposable>(new List<IDisposable> {substitute});
 
             Assert.Throws<InvalidOperationException>(() => list.ClearAndDisposeAll());
         }
diff --git a/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAllAsync.cs b/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAllAsync.cs
index 560eac7..c8b3c6a 100644
--- a/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAllAsync.cs
+++ b/X10D.Tests/src/Collections/CollectionTests.ClearAndDisposeAllAsync.cs
@@ -1,5 +1,5 @@
 using System.Collections.ObjectModel;
-using Moq;
+using NSubstitute;
 using NUnit.Framework;
 using X10D.Collections;
 
@@ -13,16 +13,17 @@ public partial class CollectionTests
         [Test]
         public async Task ClearAndDisposeAllAsync_ShouldClearAndDisposeAllItems_WhenCalledWithValidList()
         {
-            var mock1 = new Mock<IAsyncDisposable>();
-            var mock2 = new Mock<IAsyncDisposable>();
-            var mock3 = new Mock<IAsyncDisposable>();
-            var list = new List<IAsyncDisposable> {mock1.Object, mock2.Object, mock3.Object};
+            var substitute1 = Substitute.For<IAsyncDisposable>();
+            var substitute2 = Substitute.For<IAsyncDisposable>();
+            var substitute3 = Substitute.For<IAsyncDisposable>();
+            var list = new List<IAsyncDisposable> {substitute1, substitute2, substitute3};
 
             await list.ClearAndDisposeAllAsync().ConfigureAwait(false);
 
-            mock1.Verify(i => i.DisposeAsync(), Times.Once);
-            mock2.Verify(i => i.DisposeAsync(), Times.Once);
-            mock3.Verify(i => i.DisposeAsync(), Times.Once);
+            await substitute1.Received(1).DisposeAsync();
+            await substitute2.Received(1).DisposeAsync();
+            await substitute3.Received(1).DisposeAsync();
+
             Assert.That(list, Is.Empty);
         }
 
@@ -36,8 +37,8 @@ public partial class CollectionTests
         [Test]
         public void ClearAndDisposeAllAsync_ShouldThrowInvalidOperationException_WhenCalledWithReadOnlyList()
         {
-            var mock = new Mock<IAsyncDisposable>();
-            var list = new ReadOnlyCollection<IAsyncDisposable>(new List<IAsyncDisposable> {mock.Object});
+            var substitute = Substitute.For<IAsyncDisposable>();
+            var list = new ReadOnlyCollection<IAsyncDisposable>(new List<IAsyncDisposable> {substitute});
 
             Assert.ThrowsAsync<InvalidOperationException>(list.ClearAndDisposeAllAsync);
         }
diff --git a/X10D.Tests/src/Collections/EnumerableTests.DisposeAll.cs b/X10D.Tests/src/Collections/EnumerableTests.DisposeAll.cs
index d5a4b8e..a402ceb 100644
--- a/X10D.Tests/src/Collections/EnumerableTests.DisposeAll.cs
+++ b/X10D.Tests/src/Collections/EnumerableTests.DisposeAll.cs
@@ -1,4 +1,4 @@
-using Moq;
+using NSubstitute;
 using NUnit.Framework;
 using X10D.Collections;
 
@@ -12,16 +12,16 @@ public partial class EnumerableTests
         [Test]
         public void DisposeAll_ShouldDisposeAllItems_WhenCalledWithValidList()
         {
-            var mock1 = new Mock<IDisposable>();
-            var mock2 = new Mock<IDisposable>();
-            var mock3 = new Mock<IDisposable>();
-            var list = new List<IDisposable> {mock1.Object, mock2.Object, null!, mock3.Object};
+            var substitute1 = Substitute.For<IDisposable>();
+            var substitute2 = Substitute.For<IDisposable>();
+            var substitute3 = Substitute.For<IDisposable>();
+            var list = new List<IDisposable> { substitute1, substitute2, null!, substitute3 };
 
             list.DisposeAll();
 
-            mock1.Verify(i => i.Dispose(), Times.Once);
-            mock2.Verify(i => i.Dispose(), Times.Once);
-            mock3.Verify(i => i.Dispose(), Times.Once);
+            substitute1.Received(1).Dispose();
+            substitute2.Received(1).Dispose();
+            substitute3.Received(1).Dispose();
         }
 
         [Test]
diff --git a/X10D.Tests/src/Collections/EnumerableTests.DisposeAllAsync.cs b/X10D.Tests/src/Collections/EnumerableTests.DisposeAllAsync.cs
index 867006e..1510338 100644
--- a/X10D.Tests/src/Collections/EnumerableTests.DisposeAllAsync.cs
+++ b/X10D.Tests/src/Collections/EnumerableTests.DisposeAllAsync.cs
@@ -1,4 +1,4 @@
-using Moq;
+using NSubstitute;
 using NUnit.Framework;
 using X10D.Collections;
 
@@ -12,16 +12,16 @@ public partial class EnumerableTests
         [Test]
         public async Task DisposeAllAsync_ShouldDisposeAllItems_WhenCalledWithValidList()
         {
-            var mock1 = new Mock<IAsyncDisposable>();
-            var mock2 = new Mock<IAsyncDisposable>();
-            var mock3 = new Mock<IAsyncDisposable>();
-            var list = new List<IAsyncDisposable> {mock1.Object, mock2.Object, null!, mock3.Object};
+            var substitute1 = Substitute.For<IAsyncDisposable>();
+            var substitute2 = Substitute.For<IAsyncDisposable>();
+            var substitute3 = Substitute.For<IAsyncDisposable>();
+            var list = new List<IAsyncDisposable> { substitute1, substitute2, null!, substitute3 };
 
             await list.DisposeAllAsync().ConfigureAwait(false);
 
-            mock1.Verify(i => i.DisposeAsync(), Times.Once);
-            mock2.Verify(i => i.DisposeAsync(), Times.Once);
-            mock3.Verify(i => i.DisposeAsync(), Times.Once);
+            await substitute1.Received(1).DisposeAsync();
+            await substitute2.Received(1).DisposeAsync();
+            await substitute3.Received(1).DisposeAsync();
         }
 
         [Test]