diff --git a/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/ImplicitUsings.cs b/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/ImplicitUsings.cs
index 40a010c6..53091fdb 100644
--- a/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/ImplicitUsings.cs
+++ b/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/ImplicitUsings.cs
@@ -3,7 +3,7 @@
 global using ApprovalTests.Reporters;
 global using Castle.DynamicProxy.Generators.Emitters;
 global using FluentAssertions;
-global using Moq;
+global using NSubstitute;
 global using ReqnrollConnector;
 global using ReqnrollConnector.Discovery;
 global using ReqnrollConnector.Logging;
diff --git a/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/Reqnroll.VisualStudio.ReqnrollConnector.Tests.csproj b/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/Reqnroll.VisualStudio.ReqnrollConnector.Tests.csproj
index 1e09c057..e4a18cc7 100644
--- a/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/Reqnroll.VisualStudio.ReqnrollConnector.Tests.csproj
+++ b/Tests/Connector/Reqnroll.VisualStudio.ReqnrollConnector.Tests/Reqnroll.VisualStudio.ReqnrollConnector.Tests.csproj
@@ -15,7 +15,7 @@
     <PackageReference Include="ApprovalTests" Version="5.9.0" /> <!-- cannot upgrade to 6.0 because of test execution issues -->
     <PackageReference Include="FluentAssertions" Version="6.12.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
-    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="NSubstitute " Version="5.3.0" />
     <PackageReference Include="NuGet.CommandLine" Version="6.11.0" CopyTools="true" CopyToolsTarget="Tools-NuGet">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
diff --git a/Tests/Reqnroll.VisualStudio.Specs/ImplicitUsings.cs b/Tests/Reqnroll.VisualStudio.Specs/ImplicitUsings.cs
index 79bd68ef..f87e0425 100644
--- a/Tests/Reqnroll.VisualStudio.Specs/ImplicitUsings.cs
+++ b/Tests/Reqnroll.VisualStudio.Specs/ImplicitUsings.cs
@@ -6,7 +6,7 @@
 global using Microsoft.VisualStudio.Text.Editor;
 global using Microsoft.VisualStudio.Text.Tagging;
 global using Microsoft.VisualStudio.Threading;
-global using Moq;
+global using NSubstitute;
 global using Reqnroll.SampleProjectGenerator;
 global using Reqnroll.VisualStudio.Common;
 global using Reqnroll.VisualStudio.Configuration;
diff --git a/Tests/Reqnroll.VisualStudio.Specs/Reqnroll.VisualStudio.Specs.csproj b/Tests/Reqnroll.VisualStudio.Specs/Reqnroll.VisualStudio.Specs.csproj
index 83c94561..75f1af88 100644
--- a/Tests/Reqnroll.VisualStudio.Specs/Reqnroll.VisualStudio.Specs.csproj
+++ b/Tests/Reqnroll.VisualStudio.Specs/Reqnroll.VisualStudio.Specs.csproj
@@ -9,7 +9,7 @@
 
   <ItemGroup>
     <PackageReference Include="System.IO.Abstractions.TestingHelpers" Version="21.0.29" />
-    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="NSubstitute " Version="5.3.0" />
     <PackageReference Include="FluentAssertions" Version="6.12.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
     <PackageReference Include="xunit" Version="2.9.0" />
diff --git a/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/DeveroomSteps.cs b/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/DeveroomSteps.cs
index e275c27b..78bb18fe 100644
--- a/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/DeveroomSteps.cs
+++ b/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/DeveroomSteps.cs
@@ -15,11 +15,8 @@ public DeveroomSteps(ITestOutputHelper outputHelper, StubIdeScope stubIdeScope)
     {
         _outputHelper = outputHelper;
         _stubIdeScope = stubIdeScope;
-
-        _stubIdeScope.Setup(s =>
-                s.FireAndForgetOnBackgroundThread(It.IsAny<Func<CancellationToken, Task>>(), It.IsAny<string>()))
-            .Callback(FireAndForgetCallBack);
-
+        _stubIdeScope.SetupFireAndForgetOnBackgroundThread(FireAndForgetCallBack);
+        
         async void FireAndForgetCallBack(Func<CancellationToken, Task> action, string _)
         {
             try
diff --git a/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/ProjectSystemSteps.cs b/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/ProjectSystemSteps.cs
index da02879f..b6dd9d44 100644
--- a/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/ProjectSystemSteps.cs
+++ b/Tests/Reqnroll.VisualStudio.Specs/StepDefinitions/ProjectSystemSteps.cs
@@ -1,7 +1,4 @@
 #nullable disable
-using Microsoft.Build.Framework.XamlTypes;
-using ScenarioBlock = Reqnroll.VisualStudio.Editor.Services.Parser.ScenarioBlock;
-
 namespace Reqnroll.VisualStudio.Specs.StepDefinitions;
 
 [Binding]
@@ -21,10 +18,7 @@ public class ProjectSystemSteps : Steps
     public ProjectSystemSteps(StubIdeScope stubIdeScope)
     {
         _ideScope = stubIdeScope;
-        _ideScope.Setup(s =>
-                s.FireAndForgetOnBackgroundThread(It.IsAny<Func<CancellationToken, Task>>(), It.IsAny<string>()))
-            .Callback((Func<CancellationToken, Task> action, string _) =>
-                action(_ideScope.BackgroundTaskTokenSource.Token));
+        _ideScope.SetupFireAndForgetOnBackgroundThread((action, callerName) =>  action(_ideScope.BackgroundTaskTokenSource.Token));
     }
 
     private StubIdeActions ActionsMock => (StubIdeActions) _ideScope.Actions;
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Analytics/AnalyticsTransmitterTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Analytics/AnalyticsTransmitterTests.cs
index 98a8ae16..69e8110a 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Analytics/AnalyticsTransmitterTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Analytics/AnalyticsTransmitterTests.cs
@@ -6,8 +6,8 @@ namespace Reqnroll.VisualStudio.Tests.Analytics;
 
 public class AnalyticsTransmitterTests
 {
-    private Mock<IAnalyticsTransmitterSink> analyticsTransmitterSinkStub;
-    private Mock<IEnableAnalyticsChecker> enableAnalyticsCheckerStub;
+    private IAnalyticsTransmitterSink analyticsTransmitterSinkStub;
+    private IEnableAnalyticsChecker enableAnalyticsCheckerStub;
 
     [Fact]
     public void Should_NotSendAnalytics_WhenDisabled()
@@ -15,10 +15,10 @@ public void Should_NotSendAnalytics_WhenDisabled()
         var sut = CreateSut();
         GivenAnalyticsDisabled();
 
-        sut.TransmitEvent(It.IsAny<IAnalyticsEvent>());
+        sut.TransmitEvent(Substitute.For<IAnalyticsEvent>());
 
-        enableAnalyticsCheckerStub.Verify(analyticsChecker => analyticsChecker.IsEnabled(), Times.Once);
-        analyticsTransmitterSinkStub.Verify(sink => sink.TransmitEvent(It.IsAny<IAnalyticsEvent>()), Times.Never);
+        enableAnalyticsCheckerStub.Received(1).IsEnabled();
+        analyticsTransmitterSinkStub.DidNotReceive().TransmitEvent(Arg.Any<IAnalyticsEvent>());
     }
 
     [Fact]
@@ -27,10 +27,10 @@ public void Should_SendAnalytics_WhenEnabled()
         var sut = CreateSut();
         GivenAnalyticsEnabled();
 
-        sut.TransmitEvent(It.IsAny<IAnalyticsEvent>());
+        sut.TransmitEvent(Substitute.For<IAnalyticsEvent>());
 
-        enableAnalyticsCheckerStub.Verify(analyticsChecker => analyticsChecker.IsEnabled(), Times.Once);
-        analyticsTransmitterSinkStub.Verify(sink => sink.TransmitEvent(It.IsAny<IAnalyticsEvent>()), Times.Once);
+        enableAnalyticsCheckerStub.Received(1).IsEnabled();
+        analyticsTransmitterSinkStub.Received(1).TransmitEvent(Arg.Any<IAnalyticsEvent>());
     }
 
     [Theory]
@@ -44,24 +44,23 @@ public void Should_TransmitEvents(string eventName)
 
         sut.TransmitEvent(new GenericEvent(eventName));
 
-        analyticsTransmitterSinkStub.Verify(
-            sink => sink.TransmitEvent(It.Is<IAnalyticsEvent>(ae => ae.EventName == eventName)), Times.Once);
+        analyticsTransmitterSinkStub.Received(1).TransmitEvent(Arg.Is<IAnalyticsEvent>(ae => ae.EventName == eventName));
     }
 
     private void GivenAnalyticsEnabled()
     {
-        enableAnalyticsCheckerStub.Setup(analyticsChecker => analyticsChecker.IsEnabled()).Returns(true);
+        enableAnalyticsCheckerStub.IsEnabled().Returns(true);
     }
 
     private void GivenAnalyticsDisabled()
     {
-        enableAnalyticsCheckerStub.Setup(analyticsChecker => analyticsChecker.IsEnabled()).Returns(false);
+        enableAnalyticsCheckerStub.IsEnabled().Returns(false);
     }
 
     public AnalyticsTransmitter CreateSut()
     {
-        analyticsTransmitterSinkStub = new Mock<IAnalyticsTransmitterSink>();
-        enableAnalyticsCheckerStub = new Mock<IEnableAnalyticsChecker>();
-        return new AnalyticsTransmitter(analyticsTransmitterSinkStub.Object, enableAnalyticsCheckerStub.Object);
+        analyticsTransmitterSinkStub = Substitute.For<IAnalyticsTransmitterSink>();
+        enableAnalyticsCheckerStub = Substitute.For<IEnableAnalyticsChecker>();
+        return new AnalyticsTransmitter(analyticsTransmitterSinkStub, enableAnalyticsCheckerStub);
     }
 }
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Analytics/FileUserIdStoreTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Analytics/FileUserIdStoreTests.cs
index 10dfe1b9..65cbcaca 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Analytics/FileUserIdStoreTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Analytics/FileUserIdStoreTests.cs
@@ -4,7 +4,7 @@ namespace Reqnroll.VisualStudio.Tests.Analytics;
 public class FileUserIdStoreTests
 {
     private const string UserId = "491ed5c0-9f25-4c27-941a-19b17cc81c87";
-    private Mock<IFileSystemForVs> fileSystemStub;
+    private IFileSystemForVs fileSystemStub;
 
     [Fact]
     public void Should_GetUserIdFromFile_WhenFileExists()
@@ -29,30 +29,29 @@ public void Should_PersistNewlyGeneratedUserId_WhenNoUserIdExists()
         string userId = sut.GetUserId();
 
         userId.Should().NotBeEmpty();
-        fileSystemStub.Verify(fileSystem => fileSystem.File.WriteAllText(FileUserIdStore.UserIdFilePath, userId),
-            Times.Once());
+        fileSystemStub.File.Received(1).WriteAllText(FileUserIdStore.UserIdFilePath, userId);
     }
 
 
     public FileUserIdStore CreateSut()
     {
-        fileSystemStub = new Mock<IFileSystemForVs>();
-        return new FileUserIdStore(fileSystemStub.Object);
+        fileSystemStub = Substitute.For<IFileSystemForVs>();
+        return new FileUserIdStore(fileSystemStub);
     }
 
     private void GivenFileExists()
     {
-        fileSystemStub.Setup(fileSystem => fileSystem.File.Exists(It.IsAny<string>())).Returns(true);
+        fileSystemStub.File.Exists(Arg.Any<string>()).Returns(true);
     }
 
     private void GivenFileDoesNotExists()
     {
-        fileSystemStub.Setup(fileSystem => fileSystem.File.Exists(It.IsAny<string>())).Returns(false);
-        fileSystemStub.Setup(fileSystem => fileSystem.Directory.Exists(It.IsAny<string>())).Returns(true);
+        fileSystemStub.File.Exists(Arg.Any<string>()).Returns(false);
+        fileSystemStub.Directory.Exists(Arg.Any<string>()).Returns(true);
     }
 
     private void GivenUserIdStringInFile(string userIdString)
     {
-        fileSystemStub.Setup(fileSystem => fileSystem.File.ReadAllText(It.IsAny<string>())).Returns(userIdString);
+        fileSystemStub.File.ReadAllText(Arg.Any<string>()).Returns(userIdString);
     }
 }
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Discovery/DiscoveryTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Discovery/DiscoveryTests.cs
index afa388f9..c8d3ed7c 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Discovery/DiscoveryTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Discovery/DiscoveryTests.cs
@@ -21,20 +21,16 @@ public DiscoveryTests(ITestOutputHelper testOutputHelper)
 
     private Sut ArrangeSut()
     {
-        var bindingRegistryCache = new StubProjectBindingRegistryCache();
+        var bindingRegistryCache = Substitute.ForPartsOf<StubProjectBindingRegistryCache>();
         var projectScope = new InMemoryStubProjectScope(_testOutputHelper);
         var discoveryResultProvider = new StubDiscoveryResultProvider();
 #pragma warning disable VSTHRD002
-        projectScope.StubIdeScope
-            .Setup(
-                s => s.FireAndForgetOnBackgroundThread(It.IsAny<Func<CancellationToken, Task>>(), It.IsAny<string>()))
-            .Callback((Func<CancellationToken, Task> action, string _)
-                => action(projectScope.StubIdeScope.BackgroundTaskTokenSource.Token).Wait());
+        projectScope.StubIdeScope.SetupFireAndForgetOnBackgroundThread((action, callerName) => action(projectScope.StubIdeScope.BackgroundTaskTokenSource.Token).Wait());
 #pragma warning restore VSTHRD002
 
         InMemoryStubProjectBuilder.CreateOutputAssembly(projectScope);
 
-        return new Sut(bindingRegistryCache, projectScope, discoveryResultProvider);
+        return Substitute.For<Sut>(bindingRegistryCache, projectScope, discoveryResultProvider);
     }
 
     [Fact]
@@ -48,8 +44,7 @@ public void TriggerDiscoveryUpdatesTheCache()
         discoveryService.TriggerDiscovery();
 
         //assert
-        sut.BindingRegistryCache.Verify(c =>
-            c.Update(It.IsAny<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>()));
+        sut.BindingRegistryCache.Received().Update(Arg.Any<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>());
         sut.BindingRegistryCache.Value.Version.Should().NotBe(1);
     }
 
@@ -65,8 +60,7 @@ public void TriggersCacheUpdateOnEvents(LabeledTestData<Action<Sut>> triggerEven
         triggerEvent.Data(sut);
 
         //assert
-        sut.BindingRegistryCache.Verify(c =>
-            c.Update(It.IsAny<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>()));
+        sut.BindingRegistryCache.Received().Update(Arg.Any<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>());
         sut.BindingRegistryCache.Value.Version.Should().NotBe(1);
     }
 
@@ -84,9 +78,7 @@ public void DoNotTriggersCacheUpdateOnEventsForTheSameProject(LabeledTestData<Ac
         triggerEvent.Data(sut);
 
         //assert
-        sut.BindingRegistryCache.Verify(c =>
-                c.Update(It.IsAny<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>()), Times.Once,
-            "the cache update have to be called only once when the project haven't changed");
+        sut.BindingRegistryCache.Received(1).Update(Arg.Any<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>()); // the cache update have to be called only once when the project haven't changed
         sut.BindingRegistryCache.Value.Should().BeSameAs(bindingRegistry, "the cache must not be modified");
         sut.ProjectScope.StubIdeScope.StubLogger.Messages.Where(m => m == "Projects built or settings initialized")
             .Should().HaveCount(2, "the event is fired twice");
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Discovery/ProjectBindingRegistryCacheTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Discovery/ProjectBindingRegistryCacheTests.cs
index 2ac66c92..70721f44 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Discovery/ProjectBindingRegistryCacheTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Discovery/ProjectBindingRegistryCacheTests.cs
@@ -72,16 +72,16 @@ public void ParallelUpdate()
     {
         //arrange
         var start = DateTimeOffset.UtcNow;
-        var ideScope = new Mock<IIdeScope>(MockBehavior.Strict);
+        var ideScope = Substitute.For<IIdeScope>();
         var stubLogger = new StubLogger();
         var logger = new DeveroomCompositeLogger();
         logger.Add(new DeveroomXUnitLogger(_testOutputHelper));
         logger.Add(stubLogger);
 
-        ideScope.SetupGet(s => s.Logger).Returns(logger);
-        ideScope.Setup(s => s.CalculateSourceLocationTrackingPositions(It.IsAny<IEnumerable<SourceLocation>>()));
+        ideScope.Logger.Returns(logger);
+        ideScope.CalculateSourceLocationTrackingPositions(Arg.Any<IEnumerable<SourceLocation>>());
 
-        var projectBindingRegistryCache = new ProjectBindingRegistryCache(ideScope.Object);
+        var projectBindingRegistryCache = new ProjectBindingRegistryCache(ideScope);
 
         var oldVersions = new ConcurrentQueue<int>();
         var initialRegistry = new ProjectBindingRegistry(Array.Empty<ProjectStepDefinitionBinding>(), Array.Empty<ProjectHookBinding>(), 123456);
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Editor/Commands/CommentUncommentCommandTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Editor/Commands/CommentUncommentCommandTests.cs
index 93706bd5..2a6f2151 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Editor/Commands/CommentUncommentCommandTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Editor/Commands/CommentUncommentCommandTests.cs
@@ -7,7 +7,7 @@ public class CommentUncommentCommandTests
 
     public CommentUncommentCommandTests(ITestOutputHelper testOutputHelper)
     {
-        _taggerProvider = new Mock<IDeveroomTaggerProvider>().Object;
+        _taggerProvider = Substitute.For<IDeveroomTaggerProvider>();
         _ideScope = new StubIdeScope(testOutputHelper);
     }
 
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/DeveroomGherkinParserTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/DeveroomGherkinParserTests.cs
index 7f11707f..d3ccc3a9 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/DeveroomGherkinParserTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/DeveroomGherkinParserTests.cs
@@ -9,7 +9,7 @@ public class DeveroomGherkinParserTests
     public void Should_provide_parse_result_when_unexpected_end_of_file()
     {
         var sut = new DeveroomGherkinParser(new ReqnrollGherkinDialectProvider("en-US"),
-            new Mock<IMonitoringService>().Object);
+            Substitute.For<IMonitoringService>());
 
         var result = sut.ParseAndCollectErrors(@"
 Feature: Addition
@@ -24,7 +24,7 @@ public void Should_provide_parse_result_when_unexpected_end_of_file()
     public void Should_tolerate_backslash_at_end_of_line_in_DataTable()
     {
         var sut = new DeveroomGherkinParser(new ReqnrollGherkinDialectProvider("en-US"),
-            new Mock<IMonitoringService>().Object);
+            Substitute.For<IMonitoringService>());
 
         var result = sut.ParseAndCollectErrors(@"
 Feature: Addition
@@ -42,7 +42,7 @@ When I press
     public void Should_tolerate_unfinished_DataTable()
     {
         var sut = new DeveroomGherkinParser(new ReqnrollGherkinDialectProvider("en-US"),
-            new Mock<IMonitoringService>().Object);
+            Substitute.For<IMonitoringService>());
 
         var result = sut.ParseAndCollectErrors(@"
 Feature: Addition
@@ -60,7 +60,7 @@ When I press
     public void Should_provide_parse_result_when_file_ends_with_open_docstring()
     {
         var sut = new DeveroomGherkinParser(new ReqnrollGherkinDialectProvider("en-US"),
-            new Mock<IMonitoringService>().Object);
+            Substitute.For<IMonitoringService>());
 
         var result = sut.ParseAndCollectErrors(@"
 Feature: Addition
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/FeatureFileTaggerTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/FeatureFileTaggerTests.cs
index c5f6a500..ebb82dea 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/FeatureFileTaggerTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/FeatureFileTaggerTests.cs
@@ -15,8 +15,8 @@ public void Parse_triggered_in_background_after_instantiation()
         //arrange
         using var sut = TaggerSut.Arrange(_testOutputHelper);
         var parserInvoked = false;
-        sut.TagParser.Setup(s => s.Parse(It.IsAny<ITextSnapshot>()))
-            .Returns(() =>
+        sut.TagParser.Parse(Arg.Any<ITextSnapshot>())
+            .Returns(_ =>
             {
                 parserInvoked = true;
                 return ImmutableArray<DeveroomTag>.Empty;
@@ -40,11 +40,12 @@ public void GetTags_returns_with_the_parsed_values()
         IReadOnlyCollection<DeveroomTag> parseResult = ImmutableArray<DeveroomTag>.Empty;
 
         sut.TagParser
-            .Setup(s => s.Parse(It.IsAny<ITextSnapshot>()))
-            .Returns<ITextSnapshot>(snapShot =>
+            .Parse(Arg.Any<ITextSnapshot>())
+            .Returns(callInfo =>
             {
+                var snapshot = callInfo.Arg<ITextSnapshot>();
                 return parseResult = Enumerable
-                    .Repeat(() => new DeveroomTag(string.Empty, new SnapshotSpan(snapShot, 0, 0)), 10)
+                    .Repeat(() => new DeveroomTag(string.Empty, new SnapshotSpan(snapshot, 0, 0)), 10)
                     .Select(d => d())
                     .ToImmutableArray();
             });
@@ -94,13 +95,13 @@ public void Parsed_once_only_when_TextBuffer_ChangedOnBackground_fired_multiple_
         using var sut = TaggerSut.Arrange(_testOutputHelper);
 
         sut.BuildInitializedFeatureFileTagger();
-        sut.TagParser.Verify(s => s.Parse(It.IsAny<ITextSnapshot>()), Times.Once);
+        sut.TagParser.Received(1).Parse(Arg.Any<ITextSnapshot>());
 
         //act
         sut.StubTextBuffer.InvokeChangedOnBackground();
 
         //assert
-        sut.TagParser.Verify(s => s.Parse(It.IsAny<ITextSnapshot>()), Times.Exactly(2));
+        sut.TagParser.Received(2).Parse(Arg.Any<ITextSnapshot>());
     }
 
     [Fact]
@@ -112,12 +113,13 @@ public void GetTags_does_not_trigger_parse()
         IReadOnlyCollection<DeveroomTag> parseResult = ImmutableArray.Create<DeveroomTag>(VoidDeveroomTag.Instance);
 
         sut.TagParser
-            .Setup(s => s.Parse(It.IsAny<ITextSnapshot>()))
-            .Returns<ITextSnapshot>(snapShot =>
+            .Parse(Arg.Any<ITextSnapshot>())
+            .Returns(callInfo =>
             {
+                var snapshot = callInfo.Arg<ITextSnapshot>();
                 parseResult.Should().HaveCount(1, "the initial parse is called only");
                 return parseResult = Enumerable
-                    .Repeat(() => new DeveroomTag(string.Empty, new SnapshotSpan(snapShot, 0, 0)), 10)
+                    .Repeat(() => new DeveroomTag(string.Empty, new SnapshotSpan(snapshot, 0, 0)), 10)
                     .Select(d => d())
                     .ToImmutableArray();
             });
@@ -157,13 +159,14 @@ DeveroomTag TagFactory(int i, ITextSnapshot snapshot)
         }
 
         sut.TagParser
-            .Setup(s => s.Parse(It.IsAny<ITextSnapshot>()))
-            .Returns<ITextSnapshot>(snapshot =>
+            .Parse(Arg.Any<ITextSnapshot>())
+            .Returns(callInfo =>
             {
+                var snapshot = callInfo.Arg<ITextSnapshot>();
                 parseResult.Should().BeEmpty("the initial parse is called only");
                 return parseResult = Enumerable.Range(0, 10)
-                    .Select(i => TagFactory(i, snapshot))
-                    .ToImmutableArray();
+                                               .Select(i => TagFactory(i, snapshot))
+                                               .ToImmutableArray();
             });
 
         var tagger = sut.BuildInitializedFeatureFileTagger();
@@ -183,13 +186,13 @@ public void Reparse_when_binding_registry_is_changed()
     {
         //arrange
         using var sut = TaggerSut.Arrange(_testOutputHelper);
-        var discoveryService = new Mock<IDiscoveryService>(MockBehavior.Strict);
-        sut.ProjectScope.Properties.AddProperty(typeof(IDiscoveryService), discoveryService.Object);
+        var discoveryService = Substitute.For<IDiscoveryService>();
+        sut.ProjectScope.Properties.AddProperty(typeof(IDiscoveryService), discoveryService);
         sut.BuildInitializedFeatureFileTagger();
         sut.WaitForTagsChangedEvent();
 
         //act
-        discoveryService.Raise(ds => ds.WeakBindingRegistryChanged -= null!, EventArgs.Empty);
+        discoveryService.WeakBindingRegistryChanged -= Raise.Event<EventHandler<EventArgs>>(EventArgs.Empty);
 
         //assert
         sut.WaitForTagsChangedEvent().Should().HaveCount(2);
@@ -223,25 +226,26 @@ public void Deregister_events_when_TextBuffer_is_not_a_feature_file()
     {
         //arrange
         using var sut = TaggerSut.Arrange(_testOutputHelper);
-        var configurationProvider = new Mock<IDeveroomConfigurationProvider>(MockBehavior.Strict);
+        var configurationProvider = Substitute.For<IDeveroomConfigurationProvider>();
         sut.ProjectScope.Properties.RemoveProperty(typeof(IDeveroomConfigurationProvider));
-        sut.ProjectScope.Properties.AddProperty(typeof(IDeveroomConfigurationProvider), configurationProvider.Object);
-        var discoveryService = new Mock<IDiscoveryService>(MockBehavior.Strict);
-        sut.ProjectScope.Properties.AddProperty(typeof(IDiscoveryService), discoveryService.Object);
+        sut.ProjectScope.Properties.AddProperty(typeof(IDeveroomConfigurationProvider), configurationProvider);
+
+        var discoveryService = Substitute.For<IDiscoveryService>();
+        sut.ProjectScope.Properties.AddProperty(typeof(IDiscoveryService), discoveryService);
         sut.BuildFeatureFileTagger();
 
         //act
-        sut.StubTextBuffer.StubContentType = sut.StubTextBuffer.StubContentType with {TypeName = "inert"};
-        discoveryService.Raise(ds => ds.WeakBindingRegistryChanged -= null!, EventArgs.Empty);
+        sut.StubTextBuffer.StubContentType = sut.StubTextBuffer.StubContentType with { TypeName = "inert" };
+        discoveryService.WeakBindingRegistryChanged -= Raise.Event<EventHandler<EventArgs>>(EventArgs.Empty);
 
         //assert
         sut.StubTextBuffer.Properties.TryGetProperty<ITagger<DeveroomTag>>(typeof(ITagger<DeveroomTag>), out var _)
-            .Should()
-            .BeFalse();
-        discoveryService.VerifyRemove(m => m.WeakBindingRegistryChanged -= It.IsAny<EventHandler<EventArgs>>());
-        configurationProvider.VerifyRemove(m => m.WeakConfigurationChanged -= It.IsAny<EventHandler<EventArgs>>());
-        sut.StubTextBuffer.VerifyRemove(
-            tb => tb.ChangedOnBackground -= It.IsAny<EventHandler<TextContentChangedEventArgs>>());
+           .Should()
+           .BeFalse();
+
+        discoveryService.Received().WeakBindingRegistryChanged -= Arg.Any<EventHandler<EventArgs>>();
+        configurationProvider.Received().WeakConfigurationChanged -= Arg.Any<EventHandler<EventArgs>>();
+        sut.StubTextBuffer.Received().ChangedOnBackground -= Arg.Any<EventHandler<TextContentChangedEventArgs>>();
     }
 
     [Fact]
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/GherkinDocumentFormatterTests.cs b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/GherkinDocumentFormatterTests.cs
index 2754daba..32c29070 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/GherkinDocumentFormatterTests.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/GherkinDocumentFormatterTests.cs
@@ -9,13 +9,13 @@ public class GherkinDocumentFormatterTests
     private DeveroomGherkinDocument ParseGherkinDocument(TestText inputText)
     {
         var parser = new DeveroomGherkinParser(new ReqnrollGherkinDialectProvider("en-US"),
-            new Mock<IMonitoringService>().Object);
+            Substitute.For<IMonitoringService>());
         parser.ParseAndCollectErrors(inputText.ToString(), new DeveroomNullLogger(), out var gherkinDocument, out _);
         return gherkinDocument;
     }
 
     private DocumentLinesEditBuffer GetLinesBuffer(TestText inputText) =>
-        new(new Mock<ITextSnapshot>().Object, 0, inputText.Lines.Length - 1,
+        new(Substitute.For<ITextSnapshot>(), 0, inputText.Lines.Length - 1,
             inputText.Lines);
 
     [Fact]
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/TaggerSut.cs b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/TaggerSut.cs
index e94f3602..8183beb9 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/TaggerSut.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/Editor/Services/TaggerSut.cs
@@ -1,7 +1,7 @@
 namespace Reqnroll.VisualStudio.Tests.Editor.Services;
 
 public record TaggerSut
-    (IProjectScope ProjectScope, StubIdeScope IdeScope, Mock<IDeveroomTagParser> TagParser) : IDisposable
+    (IProjectScope ProjectScope, StubIdeScope IdeScope, IDeveroomTagParser TagParser) : IDisposable
 {
     private readonly ManualResetEvent _tagsChanged = new(false);
     private readonly List<SnapshotSpanEventArgs> _tagsChangedEvents = new();
@@ -27,16 +27,16 @@ public void Dispose()
     public static TaggerSut Arrange(ITestOutputHelper testOutputHelper)
     {
         var projectScope = new InMemoryStubProjectScope(testOutputHelper);
-        var tagParser = new Mock<IDeveroomTagParser>(MockBehavior.Strict);
+        var tagParser = Substitute.For<IDeveroomTagParser>();
 
         var deveroomTags = ImmutableArray<DeveroomTag>.Empty;
         tagParser
-            .Setup(s => s.Parse(It.IsAny<ITextSnapshot>()))
-            .Callback<ITextSnapshot>(fileSnapshot => { projectScope.IdeScope.Logger.Trace($"Parsing {fileSnapshot}"); })
-            .Returns(deveroomTags);
+            .Parse(Arg.Any<ITextSnapshot>())
+            .Returns(deveroomTags)
+            .AndDoes(callInfo => { projectScope.IdeScope.Logger.Trace($"Parsing {callInfo.Arg<ITextSnapshot>()}"); });
 
         projectScope.StubIdeScope.TextViewFactory =
-            (inputText, filePath) => new StubWpfTextView(new StubTextBuffer(projectScope));
+            (inputText, filePath) => new StubWpfTextView(Substitute.ForPartsOf<StubTextBuffer>(projectScope));
 
         var sut = new TaggerSut(projectScope, projectScope.StubIdeScope, tagParser);
 
@@ -54,7 +54,7 @@ public ITagger<DeveroomTag> BuildInitializedFeatureFileTagger()
 
     public ITagger<DeveroomTag> BuildFeatureFileTagger()
     {
-        ProjectScope.Properties.AddProperty(typeof(IDeveroomTagParser), TagParser.Object);
+        ProjectScope.Properties.AddProperty(typeof(IDeveroomTagParser), TagParser);
         var taggerProvider = new DeveroomTaggerProvider(IdeScope, new SpecFlowExtensionDetection.SpecFlowExtensionDetectionService(IdeScope));
 
         var tagger = BuildTagger<FeatureFileTagger>(taggerProvider);
@@ -69,7 +69,7 @@ private T BuildTagger<T>(DeveroomTaggerProvider taggerProvider) where T : ITagge
         IdeScope.CreateTextView(new TestText(Array.Empty<string>()),
             IdeScope.ProjectScopes.Select(p => p.ProjectFullName).DefaultIfEmpty(string.Empty).Single());
 
-        var tagger = (T) taggerProvider.CreateTagger<DeveroomTag>(IdeScope.CurrentTextView.TextBuffer);
+        var tagger = (T)taggerProvider.CreateTagger<DeveroomTag>(IdeScope.CurrentTextView.TextBuffer);
 
         return tagger;
     }
@@ -109,19 +109,17 @@ public TaggerSut WithRealDeveroomTagParser()
         var discoveryService = ProjectScope.GetDiscoveryService();
         var realParser = new DeveroomTagParser(IdeScope.Logger, IdeScope.MonitoringService,
             deveroomConfigurationProvider, discoveryService);
-        var tagParserMock = new Mock<IDeveroomTagParser>(MockBehavior.Strict);
-        tagParserMock.Setup(s => s.Parse(
-                It.IsAny<ITextSnapshot>()))
-            .Returns((ITextSnapshot fileSnapshot)
-                => realParser.Parse(fileSnapshot));
+        var tagParserMock = Substitute.For<IDeveroomTagParser>();
+        tagParserMock.Parse(Arg.Any<ITextSnapshot>())
+            .Returns(callInfo => realParser.Parse(callInfo.Arg<ITextSnapshot>()));
 
-        return this with {TagParser = tagParserMock};
+        return this with { TagParser = tagParserMock };
     }
 
     public TaggerSut WithoutProject()
     {
         var voidProjectScope = new VoidProjectScope(IdeScope);
-        var withoutProject = this with {ProjectScope = voidProjectScope};
+        var withoutProject = this with { ProjectScope = voidProjectScope };
         IdeScope.ProjectScopes.Clear();
         IdeScope.TextViewFactory =
             (inputText, filePath) => new StubWpfTextView(new StubTextBuffer(voidProjectScope));
diff --git a/Tests/Reqnroll.VisualStudio.Tests/ImplicitUsings.cs b/Tests/Reqnroll.VisualStudio.Tests/ImplicitUsings.cs
index 41f2c6b0..c13241be 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/ImplicitUsings.cs
+++ b/Tests/Reqnroll.VisualStudio.Tests/ImplicitUsings.cs
@@ -10,7 +10,7 @@
 global using Microsoft.VisualStudio.Text.Tagging;
 global using Microsoft.VisualStudio.TextManager.Interop;
 global using Microsoft.VisualStudio.Utilities;
-global using Moq;
+global using NSubstitute;
 global using Reqnroll.VisualStudio.Analytics;
 global using Reqnroll.VisualStudio.Common;
 global using Reqnroll.VisualStudio.Configuration;
diff --git a/Tests/Reqnroll.VisualStudio.Tests/Reqnroll.VisualStudio.Tests.csproj b/Tests/Reqnroll.VisualStudio.Tests/Reqnroll.VisualStudio.Tests.csproj
index 6d3efd51..69f8a1b0 100644
--- a/Tests/Reqnroll.VisualStudio.Tests/Reqnroll.VisualStudio.Tests.csproj
+++ b/Tests/Reqnroll.VisualStudio.Tests/Reqnroll.VisualStudio.Tests.csproj
@@ -12,7 +12,7 @@
   <ItemGroup>
     <PackageReference Include="ApprovalTests" Version="5.9.0" /> <!-- cannot upgrade to 6.0 because of test execution issues -->
     <PackageReference Include="System.IO.Abstractions.TestingHelpers" Version="21.0.29" />
-    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="NSubstitute " Version="5.3.0" />
     <PackageReference Include="FluentAssertions" Version="6.12.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
     <PackageReference Include="xunit" Version="2.9.0" />
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/ImplicitUsings.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/ImplicitUsings.cs
index febd9c68..f95b2e1f 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/ImplicitUsings.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/ImplicitUsings.cs
@@ -9,7 +9,7 @@
 global using Microsoft.VisualStudio.TextManager.Interop;
 global using Microsoft.VisualStudio.Threading;
 global using Microsoft.VisualStudio.Utilities;
-global using Moq;
+global using NSubstitute;
 global using Reqnroll.VisualStudio.Analytics;
 global using Reqnroll.VisualStudio.Annotations;
 global using Reqnroll.VisualStudio.Common;
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/InMemoryStubProjectScope.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/InMemoryStubProjectScope.cs
index 7e3baf8d..295d86df 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/InMemoryStubProjectScope.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/InMemoryStubProjectScope.cs
@@ -1,6 +1,6 @@
 namespace Reqnroll.VisualStudio.VsxStubs.ProjectSystem;
 
-public class InMemoryStubProjectScope : Mock<IProjectScope>, IProjectScope
+public class InMemoryStubProjectScope : IProjectScope
 {
     public List<NuGetPackageReference> PackageReferencesList = new();
 
@@ -82,4 +82,4 @@ public InMemoryStubProjectScope UpdateConfigFile(string configFileName, string c
         IdeScope.FileSystem.File.SetLastWriteTimeUtc(configFileFullPath, DateTime.UtcNow);
         return this;
     }
-}
+}
\ No newline at end of file
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubIdeScope.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubIdeScope.cs
index 44ad0e99..37d113c4 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubIdeScope.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubIdeScope.cs
@@ -1,15 +1,19 @@
 namespace Reqnroll.VisualStudio.VsxStubs.ProjectSystem;
 
-public class StubIdeScope : Mock<IIdeScope>, IIdeScope, IDisposable
+public class StubIdeScope : IIdeScope, IDisposable
 {
-    public StubIdeScope(ITestOutputHelper testOutputHelper) : base(MockBehavior.Strict)
+    private readonly IIdeScope _substitute;
+
+    public StubIdeScope(ITestOutputHelper testOutputHelper)
     {
+        _substitute = Substitute.For<IIdeScope>();
+
         AnalyticsTransmitter = new StubAnalyticsTransmitter(Logger);
         MonitoringService =
             new MonitoringService(
                 AnalyticsTransmitter,
-                new Mock<IWelcomeService>().Object,
-                new Mock<ITelemetryConfigurationHolder>().Object);
+                Substitute.For<IWelcomeService>(),
+                Substitute.For<ITelemetryConfigurationHolder>());
 
         CompositeLogger.Add(new DeveroomXUnitLogger(testOutputHelper));
         CompositeLogger.Add(StubLogger);
@@ -17,9 +21,9 @@ public StubIdeScope(ITestOutputHelper testOutputHelper) : base(MockBehavior.Stri
         VsxStubObjects.Initialize();
 
         SetupFireAndForget();
-        SetupFireAndForgetOnBackgroundThread();
+        SetupFireAndForgetOnBackgroundThread((action, callerName) => BackGroundTasks = BackGroundTasks.Add($"{Interlocked.Increment(ref _taskId)}:{callerName}", action));
 
-        CurrentTextView = new Mock<IWpfTextView>(MockBehavior.Strict).Object;
+        CurrentTextView = Substitute.For<IWpfTextView>();
         TextViewFactory = (inputText, filePath) =>
             BasicTextViewFactory(inputText, filePath, VsContentTypes.FeatureFile);
         BackgroundTaskTokenSource = new DebuggableCancellationTokenSource(TimeSpan.FromSeconds(20));
@@ -64,7 +68,7 @@ public IProjectScope GetProject(ITextBuffer textBuffer) =>
     public IFileSystemForVs FileSystem { get; private set; } = new MockFileSystemForVs();
 
     public IDeveroomOutputPaneServices DeveroomOutputPaneServices { get; } =
-        new Mock<IDeveroomOutputPaneServices>().Object;
+        Substitute.For<IDeveroomOutputPaneServices>();
 
     public IDeveroomErrorListServices DeveroomErrorListServices => StubErrorListServices;
     public IMonitoringService MonitoringService { get; }
@@ -84,7 +88,7 @@ public bool GetTextBuffer(SourceLocation sourceLocation, out ITextBuffer textBuf
             return true;
         }
 
-        textBuffer = new Mock<ITextBuffer>(MockBehavior.Strict).Object;
+        textBuffer = Substitute.For<ITextBuffer>();
         return false;
     }
 
@@ -96,19 +100,18 @@ public SyntaxTree GetSyntaxTree(ITextBuffer textBuffer)
 
     public void FireAndForget(Func<Task> action, Action<Exception> onException,
         [CallerMemberName] string callerName = "???")
-        => Object.FireAndForget(action, onException, callerName);
+        => _substitute.FireAndForget(action, onException, callerName);
 
     private void SetupFireAndForget()
     {
-        Setup(s => s.FireAndForget(It.IsAny<Func<Task>>(), It.IsAny<Action<Exception>>(),
-                It.IsAny<string>()))
-            .Callback((Func<Task> action, Action<Exception> onException, string _) =>
+        _substitute.When(s => s.FireAndForget(Arg.Any<Func<Task>>(), Arg.Any<Action<Exception>>(), Arg.Any<string>()))
+            .Do(callInfo =>
             {
+                var action = callInfo.Arg<Func<Task>>();
+                var onException = callInfo.Arg<Action<Exception>>();
                 try
                 {
-#pragma warning disable VSTHRD002
                     action().Wait();
-#pragma warning restore
                 }
                 catch (Exception e)
                 {
@@ -119,7 +122,7 @@ private void SetupFireAndForget()
     }
 
     public void FireAndForgetOnBackgroundThread(Func<CancellationToken, Task> action, string callerName = "???") =>
-        Object.FireAndForgetOnBackgroundThread(action, callerName);
+        _substitute.FireAndForgetOnBackgroundThread(action, callerName);
 
     private volatile int _taskId;
 
@@ -134,11 +137,15 @@ public Task StartAndWaitAllBackgroundTasks()
         return Task.WhenAll(allTasks);
     }
 
-    private void SetupFireAndForgetOnBackgroundThread()
+    public void SetupFireAndForgetOnBackgroundThread(Action<Func<CancellationToken, Task>, string> callback)
     {
-        Setup(s => s.FireAndForgetOnBackgroundThread(It.IsAny<Func<CancellationToken, Task>>(), It.IsAny<string>()))
-            .Callback((Func<CancellationToken, Task> action, string callerName) =>
-                BackGroundTasks = BackGroundTasks.Add($"{Interlocked.Increment(ref _taskId)}:{callerName}", action));
+        _substitute.When(s => s.FireAndForgetOnBackgroundThread(Arg.Any<Func<CancellationToken, Task>>(), Arg.Any<string>()))
+            .Do(callInfo =>
+            {
+                var action = callInfo.Arg<Func<CancellationToken, Task>>();
+                var callerName = callInfo.Arg<string>();
+                callback(action, callerName);
+            });
     }
 
     public Task RunOnUiThread(Action action)
@@ -158,7 +165,7 @@ public void OpenIfNotOpened(string path)
 
     public IProjectScope[] GetProjectsWithFeatureFiles() => ProjectScopes.ToArray();
 
-    public IDisposable CreateUndoContext(string undoLabel) => new Mock<IDisposable>().Object;
+    public IDisposable CreateUndoContext(string undoLabel) => Substitute.For<IDisposable>();
 
     public IWpfTextView CreateTextView(TestText inputText, string filePath)
     {
@@ -197,4 +204,4 @@ public void Dispose()
         BackgroundTaskTokenSource.Cancel();
         BackgroundTaskTokenSource.Dispose();
     }
-}
+}
\ No newline at end of file
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubProjectSettingsProvider.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubProjectSettingsProvider.cs
index 6e09df4c..b3995cde 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubProjectSettingsProvider.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/ProjectSystem/StubProjectSettingsProvider.cs
@@ -1,8 +1,8 @@
 namespace Reqnroll.VisualStudio.VsxStubs.ProjectSystem;
 
-public class StubProjectSettingsProvider : Mock<IProjectSettingsProvider>, IProjectSettingsProvider
+public class StubProjectSettingsProvider : IProjectSettingsProvider
 {
-    public StubProjectSettingsProvider(InMemoryStubProjectScope inMemoryStubProjectScope) : base(MockBehavior.Strict)
+    public StubProjectSettingsProvider(InMemoryStubProjectScope inMemoryStubProjectScope)
     {
         ProjectSettings = new ProjectSettings(
             DeveroomProjectKind.ReqnrollTestProject,
@@ -17,9 +17,6 @@ public StubProjectSettingsProvider(InMemoryStubProjectScope inMemoryStubProjectS
             ReqnrollProjectTraits.CucumberExpression,
             ProjectProgrammingLanguage.CSharp
         );
-
-        Setup(p => p.GetProjectSettings()).Returns(() => ProjectSettings);
-        Setup(p => p.CheckProjectSettings()).Returns(() => ProjectSettings);
     }
 
     private ProjectSettings ProjectSettings { get; set; }
@@ -27,17 +24,17 @@ public StubProjectSettingsProvider(InMemoryStubProjectScope inMemoryStubProjectS
     public DeveroomProjectKind Kind
     {
         get => ProjectSettings.Kind;
-        set => ProjectSettings = ProjectSettings with {Kind = value};
+        set => ProjectSettings = ProjectSettings with { Kind = value };
     }
 
     public event EventHandler<EventArgs>? WeakSettingsInitialized;
     public event EventHandler<EventArgs>? SettingsInitialized;
 
-    public ProjectSettings GetProjectSettings() => Object.GetProjectSettings();
-    public ProjectSettings CheckProjectSettings() => Object.CheckProjectSettings();
+    public ProjectSettings GetProjectSettings() => ProjectSettings;
+    public ProjectSettings CheckProjectSettings() => ProjectSettings;
 
     public void InvokeWeakSettingsInitializedEvent()
     {
-        WeakSettingsInitialized!.Invoke(this, EventArgs.Empty);
+        WeakSettingsInitialized?.Invoke(this, EventArgs.Empty);
     }
 }
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/Reqnroll.VisualStudio.VsxStubs.csproj b/Tests/Reqnroll.VisualStudio.VsxStubs/Reqnroll.VisualStudio.VsxStubs.csproj
index 6ac357af..52ca9479 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/Reqnroll.VisualStudio.VsxStubs.csproj
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/Reqnroll.VisualStudio.VsxStubs.csproj
@@ -11,7 +11,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="NSubstitute " Version="5.3.0" />
     <PackageReference Include="FluentAssertions" Version="6.12.1" />
     <PackageReference Include="System.IO.Abstractions.TestingHelpers" Version="21.0.29" />
     <PackageReference Include="xunit.abstractions" Version="2.0.3" />
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/StepDefinitions/MockableDiscoveryService.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/StepDefinitions/MockableDiscoveryService.cs
index 1ca3c67d..36bc1da4 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/StepDefinitions/MockableDiscoveryService.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/StepDefinitions/MockableDiscoveryService.cs
@@ -6,8 +6,8 @@ namespace Reqnroll.VisualStudio.VsxStubs.StepDefinitions;
 public class MockableDiscoveryService : DiscoveryService
 {
     public MockableDiscoveryService(IProjectScope projectScope,
-        Mock<IDiscoveryResultProvider> discoveryResultProviderMock)
-        : base(projectScope, discoveryResultProviderMock.Object, new ProjectBindingRegistryCache(projectScope.IdeScope))
+        IDiscoveryResultProvider discoveryResultProviderMock)
+        : base(projectScope, discoveryResultProviderMock, new ProjectBindingRegistryCache(projectScope.IdeScope))
     {
     }
 
@@ -23,7 +23,7 @@ public static MockableDiscoveryService Setup(IProjectScope projectScope, TimeSpa
     public static MockableDiscoveryService SetupWithInitialStepDefinitions(IProjectScope projectScope,
         StepDefinition[] stepDefinitions, TimeSpan discoveryDelay)
     {
-        var discoveryResultProviderMock = new Mock<IDiscoveryResultProvider>(MockBehavior.Strict);
+        var discoveryResultProviderMock = Substitute.For<IDiscoveryResultProvider>();
 
         var allStepDefinitions = new List<StepDefinition>();
         foreach (var stepDefinition in stepDefinitions)
@@ -60,8 +60,8 @@ public static MockableDiscoveryService SetupWithInitialStepDefinitions(IProjectS
         InMemoryStubProjectBuilder.CreateOutputAssembly(projectScope);
 
         discoveryResultProviderMock
-            .Setup(ds => ds.RunDiscovery(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<ProjectSettings>()))
-            .Returns(() =>
+            .RunDiscovery(Arg.Any<string>(), Arg.Any<string>(), Arg.Any<ProjectSettings>())
+            .Returns(_ =>
             {
                 Thread.Sleep(discoveryDelay); //make it a bit more realistic
                 return discoveryService.LastDiscoveryResult;
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/StubProjectBindingRegistryCache.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/StubProjectBindingRegistryCache.cs
index 8d87a58a..90da42e9 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/StubProjectBindingRegistryCache.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/StubProjectBindingRegistryCache.cs
@@ -1,28 +1,30 @@
 #nullable enable
 namespace Reqnroll.VisualStudio.VsxStubs;
 
-public class StubProjectBindingRegistryCache : Mock<IProjectBindingRegistryCache>, IProjectBindingRegistryCache
+public class StubProjectBindingRegistryCache : IProjectBindingRegistryCache
 {
-    public StubProjectBindingRegistryCache() : base(MockBehavior.Strict)
+    private readonly IProjectBindingRegistryCache _substitute;
+
+    public StubProjectBindingRegistryCache()
     {
+        _substitute = Substitute.For<IProjectBindingRegistryCache>();
+
         Value = ProjectBindingRegistry.Invalid;
-        Setup(c => c.Update(It.IsAny<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>()))
-            .Returns(async (Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>> updateFunc) =>
-            {
-                Value = await updateFunc(Value);
-                return Task.FromResult(Value);
-            });
+        _substitute.Update(Arg.Any<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>())
+                   .Returns(async callInfo =>
+                   {
+                       var updateFunc = callInfo.Arg<Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>>>();
+                       Value = await updateFunc(Value);
+                   });
     }
 
-    public bool Processing { get; }
-
     public event EventHandler<EventArgs>? Changed;
 
     public Task Update(Func<ProjectBindingRegistry, ProjectBindingRegistry> updateFunc)
         => Update(registry => Task.FromResult(updateFunc(registry)));
 
     public Task Update(Func<ProjectBindingRegistry, Task<ProjectBindingRegistry>> updateTask)
-        => Object.Update(updateTask);
+        => _substitute.Update(updateTask);
 
     public ProjectBindingRegistry Value { get; private set; }
     public Task<ProjectBindingRegistry> GetLatest() => throw new NotImplementedException();
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextBuffer.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextBuffer.cs
index a52de2a0..77416e63 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextBuffer.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextBuffer.cs
@@ -1,20 +1,26 @@
 namespace Reqnroll.VisualStudio.VsxStubs;
 
-public class StubTextBuffer : Mock<ITextBuffer2>, ITextBuffer2
+public class StubTextBuffer : ITextBuffer2
 {
-    public StubTextBuffer(IProjectScope projectScope) : base(MockBehavior.Strict)
+    private readonly ITextBuffer2 _substitute;
+
+    public StubTextBuffer(IProjectScope projectScope)
     {
+        _substitute = Substitute.For<ITextBuffer2>();
+
         Properties = new PropertyCollection();
         Properties.AddProperty(typeof(IProjectScope), projectScope);
         CurrentStubSnapshot = StubTextSnapshot.FromTextBuffer(this);
 
-        var contentType = new Mock<IContentType>(MockBehavior.Strict);
-        contentType.Setup(t => t.IsOfType(VsContentTypes.FeatureFile)).Returns(true);
-        StubContentType = new StubContentType(Array.Empty<IContentType>(), VsContentTypes.FeatureFile,
-            VsContentTypes.FeatureFile);
+        var contentType = Substitute.For<IContentType>();
+        contentType.IsOfType(VsContentTypes.FeatureFile).Returns(true);
+        StubContentType = new StubContentType(Array.Empty<IContentType>(), VsContentTypes.FeatureFile, VsContentTypes.FeatureFile);
+
+        _substitute.When(tb => tb.ChangedOnBackground += Arg.Any<EventHandler<TextContentChangedEventArgs>>())
+                   .Do(info => _changedOnBackground += info.Arg<EventHandler<TextContentChangedEventArgs>>());
 
-        SetupAdd(tb => tb.ChangedOnBackground += It.IsAny<EventHandler<TextContentChangedEventArgs>>());
-        SetupRemove(tb => tb.ChangedOnBackground -= It.IsAny<EventHandler<TextContentChangedEventArgs>>());
+        _substitute.When(tb => tb.ChangedOnBackground -= Arg.Any<EventHandler<TextContentChangedEventArgs>>())
+                   .Do(info => _changedOnBackground -= info.Arg<EventHandler<TextContentChangedEventArgs>>());
     }
 
     public StubContentType StubContentType { get; set; }
@@ -71,16 +77,8 @@ public void ChangeContentType(IContentType newContentType, object editTag)
 
     public event EventHandler<TextContentChangedEventArgs>? ChangedOnBackground
     {
-        add
-        {
-            Object.ChangedOnBackground += value;
-            _changedOnBackground += value;
-        }
-        remove
-        {
-            Object.ChangedOnBackground -= value;
-            _changedOnBackground -= value;
-        }
+        add => _substitute.ChangedOnBackground += value;
+        remove => _substitute.ChangedOnBackground -= value;
     }
 
     private event EventHandler<TextContentChangedEventArgs>? _changedOnBackground;
@@ -111,4 +109,4 @@ public void ModifyContent(string content)
     {
         CurrentStubSnapshot = CurrentStubSnapshot.WithText(content);
     }
-}
+}
\ No newline at end of file
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextSnapshot.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextSnapshot.cs
index 728f323f..10fc42dd 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextSnapshot.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextSnapshot.cs
@@ -86,13 +86,13 @@ public void SaveToFile(string filePath, bool replaceFile, Encoding encoding)
 
     public static StubTextSnapshot FromTextBuffer(ITextBuffer textBuffer) =>
         new(
-            Mock.Of<IContentType>(MockBehavior.Strict),
+            Substitute.For<IContentType>(),
             0,
             0,
             Array.Empty<ITextSnapshotLine>(),
             textBuffer,
             StubTextVersion2.Default with {TextBuffer = textBuffer},
-            Mock.Of<ITextImage>(MockBehavior.Strict),
+            Substitute.For<ITextImage>(),
             new TestText());
 
     public StubTextSnapshot WithText(string testText)
diff --git a/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextVersion2.cs b/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextVersion2.cs
index fbb1d937..9b059888 100644
--- a/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextVersion2.cs
+++ b/Tests/Reqnroll.VisualStudio.VsxStubs/StubTextVersion2.cs
@@ -10,10 +10,10 @@ public record StubTextVersion2(
     : ITextVersion2
 {
     public static StubTextVersion2 Default = new(
-        Mock.Of<INormalizedTextChangeCollection>(m => m.Count == 0, MockBehavior.Strict),
+        Substitute.For<INormalizedTextChangeCollection>(),
         0,
-        0, Mock.Of<ITextBuffer>(MockBehavior.Strict),
-        0, Mock.Of<ITextImageVersion>(MockBehavior.Strict));
+        0, Substitute.For<ITextBuffer>(),
+        0, Substitute.For<ITextImageVersion>());
 
     [CanBeNull] public ITextVersion Next { get; private set; } = null!;