diff --git a/Libraries.sln b/Libraries.sln
index 6637cd4..4b386ae 100644
--- a/Libraries.sln
+++ b/Libraries.sln
@@ -3,11 +3,11 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.9.34321.82
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Vivelin.Core", "src\Vivelin.Core\Vivelin.Core.csproj", "{086D3637-D9E3-4980-8C50-1ABDFA99AAF3}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Vivelin.Core", "src\Vivelin.Core\Vivelin.Core.csproj", "{086D3637-D9E3-4980-8C50-1ABDFA99AAF3}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Tests", "Tests", "{55F80F8C-2CFB-4E4B-A4C7-373376BB8BF5}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Vivelin.Core.Tests", "tests\Vivelin.Core.Tests\Vivelin.Core.Tests.csproj", "{2E7E3540-851C-4351-8644-B9F946E9F42E}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Vivelin.Core.Tests", "tests\Vivelin.Core.Tests\Vivelin.Core.Tests.csproj", "{2E7E3540-851C-4351-8644-B9F946E9F42E}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
diff --git a/tests/Vivelin.Core.Tests/GlobalUsings.cs b/tests/Vivelin.Core.Tests/GlobalUsings.cs
index d6558d2..ae1f867 100644
--- a/tests/Vivelin.Core.Tests/GlobalUsings.cs
+++ b/tests/Vivelin.Core.Tests/GlobalUsings.cs
@@ -1,3 +1,3 @@
 global using Xunit;
 global using FluentAssertions;
-global using Moq;
\ No newline at end of file
+global using NSubstitute;
\ No newline at end of file
diff --git "a/tests/Vivelin.Core.Tests/Schr\303\266dingerTests.cs" "b/tests/Vivelin.Core.Tests/Schr\303\266dingerTests.cs"
index d9f44e4..f1aff9f 100644
--- "a/tests/Vivelin.Core.Tests/Schr\303\266dingerTests.cs"
+++ "b/tests/Vivelin.Core.Tests/Schr\303\266dingerTests.cs"
@@ -7,9 +7,10 @@ public void SchrodingersString_ResolvesToRandomString()
     {
         var values = new[] { "Bulbasaur", "Charmander", "Squirtle" };
         var instance = new Schrödinger<string>(values);
-        var mockRandom = Mock.Of<Random>(x => x.Next(2) == 0);
+        var random = Substitute.For<Random>();
+        random.Next(2).Returns(0);
 
-        instance.Resolve(mockRandom).Should().Be("Bulbasaur");
+        instance.Resolve(random).Should().Be("Bulbasaur");
     }
 
     [Fact]
diff --git a/tests/Vivelin.Core.Tests/Vivelin.Core.Tests.csproj b/tests/Vivelin.Core.Tests/Vivelin.Core.Tests.csproj
index f1faf04..c9df006 100644
--- a/tests/Vivelin.Core.Tests/Vivelin.Core.Tests.csproj
+++ b/tests/Vivelin.Core.Tests/Vivelin.Core.Tests.csproj
@@ -12,7 +12,7 @@
   <ItemGroup>
     <PackageReference Include="FluentAssertions" Version="6.12.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.0" />
-    <PackageReference Include="Moq" Version="4.20.69" />
+    <PackageReference Include="NSubstitute" Version="5.1.0" />
     <PackageReference Include="xunit" Version="2.4.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>