diff --git a/tests/CodeMeridian.Application.Tests/CodeMeridian.Application.Tests.csproj b/tests/CodeMeridian.Application.Tests/CodeMeridian.Application.Tests.csproj
index b3679ec9..1a51e74a 100644
--- a/tests/CodeMeridian.Application.Tests/CodeMeridian.Application.Tests.csproj
+++ b/tests/CodeMeridian.Application.Tests/CodeMeridian.Application.Tests.csproj
@@ -17,7 +17,7 @@
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     <PackageReference Include="xunit.runner.visualstudio" Version="3.*" />
-    <PackageReference Include="NSubstitute" Version="5.*" />
+    <PackageReference Include="NSubstitute" Version="6.*" />
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 </Project>
diff --git a/tests/CodeMeridian.Indexer.Tests/CodeMeridian.Indexer.Tests.csproj b/tests/CodeMeridian.Indexer.Tests/CodeMeridian.Indexer.Tests.csproj
index 361d8114..b9634b1a 100644
--- a/tests/CodeMeridian.Indexer.Tests/CodeMeridian.Indexer.Tests.csproj
+++ b/tests/CodeMeridian.Indexer.Tests/CodeMeridian.Indexer.Tests.csproj
@@ -17,6 +17,6 @@
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     <PackageReference Include="FluentAssertions" Version="7.*" />
-    <PackageReference Include="NSubstitute" Version="5.*" />
+    <PackageReference Include="NSubstitute" Version="6.*" />
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 </Project>
diff --git a/tests/CodeMeridian.Infrastructure.Tests/CodeMeridian.Infrastructure.Tests.csproj b/tests/CodeMeridian.Infrastructure.Tests/CodeMeridian.Infrastructure.Tests.csproj
index 1915cf30..814e17c1 100644
--- a/tests/CodeMeridian.Infrastructure.Tests/CodeMeridian.Infrastructure.Tests.csproj
+++ b/tests/CodeMeridian.Infrastructure.Tests/CodeMeridian.Infrastructure.Tests.csproj
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-    <PackageReference Include="NSubstitute" Version="5.*" />
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diff --git a/tests/CodeMeridian.McpServer.Tests/CodeMeridian.McpServer.Tests.csproj b/tests/CodeMeridian.McpServer.Tests/CodeMeridian.McpServer.Tests.csproj
index e3580427..446418dd 100644
--- a/tests/CodeMeridian.McpServer.Tests/CodeMeridian.McpServer.Tests.csproj
+++ b/tests/CodeMeridian.McpServer.Tests/CodeMeridian.McpServer.Tests.csproj
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