diff --git a/CHANGELOG.md b/CHANGELOG.md
index 603269a..e7ae2a5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,2 +1,5 @@
 2025-05-18 Added unit tests for InternalExtensions
   - Build failed: unable to restore NuGet packages offline
+
+2025-05-19 Added tests for ServiceCollectionExtensions
+  - Fixed build and enabled unit tests
\ No newline at end of file
diff --git a/DevDistricts.Tests/DevDistricts.Tests.csproj b/DevDistricts.Tests/DevDistricts.Tests.csproj
index a7eec33..8c30adf 100644
--- a/DevDistricts.Tests/DevDistricts.Tests.csproj
+++ b/DevDistricts.Tests/DevDistricts.Tests.csproj
@@ -9,6 +9,7 @@
 
   <ItemGroup>
     <PackageReference Include="coverlet.collector" Version="6.0.2" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.5" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="xunit" Version="2.9.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
diff --git a/DevDistricts.Tests/ServiceCollectionExtensionsTests.cs b/DevDistricts.Tests/ServiceCollectionExtensionsTests.cs
new file mode 100644
index 0000000..e2e9d3c
--- /dev/null
+++ b/DevDistricts.Tests/ServiceCollectionExtensionsTests.cs
@@ -0,0 +1,57 @@
+using System;
+using System.Linq;
+using DevDistricts;
+using DevDistricts.Internal;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Xunit;
+
+[District(DependencyInjectionTypes = new[] { typeof(SampleService) })]
+[Occupant(UserName = "user", MachineName = "machine")]
+internal class SampleDistrict
+{
+}
+
+internal class SampleService
+{
+}
+
+public class ServiceCollectionExtensionsTests
+{
+    [Fact]
+    public void WithDevDistricts_RegistersHostedService_AndInvokesCallback()
+    {
+        var services = new ServiceCollection();
+        Type[]? callbackTypes = null;
+
+        services.WithDevDistricts(o => o
+            .WithUserName("user")
+            .WithMachineName("machine")
+            .WithDependencyInjectionCallback(types => callbackTypes = types.ToArray()));
+
+        var descriptor = services.Single(d => d.ServiceType == typeof(IHostedService));
+        Assert.Equal(typeof(DistrictRunner<SampleDistrict>), descriptor.ImplementationType);
+        Assert.NotNull(callbackTypes);
+        Assert.Contains(typeof(SampleService), callbackTypes);
+    }
+
+    [Fact]
+    public void WithDevDistricts_Throws_NoMatchingDistrictException_When_No_District()
+    {
+        var services = new ServiceCollection();
+        Assert.Throws<NoMatchingDistrictException>(() =>
+            services.WithDevDistricts(o => o
+                .WithUserName("none")
+                .WithMachineName("none")));
+    }
+
+    [Fact]
+    public void WithDevDistricts_Throws_NotSupported_When_DITypes_NoCallback()
+    {
+        var services = new ServiceCollection();
+        Assert.Throws<NotSupportedException>(() =>
+            services.WithDevDistricts(o => o
+                .WithUserName("user")
+                .WithMachineName("machine")));
+    }
+}
diff --git a/DevDistricts.sln.DotSettings.user b/DevDistricts.sln.DotSettings.user
new file mode 100644
index 0000000..7930c35
--- /dev/null
+++ b/DevDistricts.sln.DotSettings.user
@@ -0,0 +1,4 @@
+<wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
+	<s:String x:Key="/Default/Environment/UnitTesting/UnitTestSessionStore/Sessions/=35e304cf_002D645f_002D44d8_002Da369_002D19333fcf2e8c/@EntryIndexedValue">&lt;SessionState ContinuousTestingMode="0" IsActive="True" Name="All tests from &amp;lt;DevDistricts.Tests&amp;gt;" xmlns="urn:schemas-jetbrains-com:jetbrains-ut-session"&gt;&#xD;
+  &lt;Project Location="E:\Projects\DevDistricts\DevDistricts.Tests" Presentation="&amp;lt;DevDistricts.Tests&amp;gt;" /&gt;&#xD;
+&lt;/SessionState&gt;</s:String></wpf:ResourceDictionary>
\ No newline at end of file
diff --git a/DevDistricts/AssemblyInfo.cs b/DevDistricts/AssemblyInfo.cs
new file mode 100644
index 0000000..e10192a
--- /dev/null
+++ b/DevDistricts/AssemblyInfo.cs
@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("DevDistricts.Tests")]
diff --git a/DevDistricts/DevDistricts.csproj b/DevDistricts/DevDistricts.csproj
index dea3c0a..8ca62f4 100644
--- a/DevDistricts/DevDistricts.csproj
+++ b/DevDistricts/DevDistricts.csproj
@@ -2,6 +2,7 @@
 
     <PropertyGroup>
         <TargetFramework>netstandard2.0</TargetFramework>
+        <LangVersion>latestMajor</LangVersion>
         <Nullable>enable</Nullable>
         <PackageLicenseUrl>https://github.com/akrock/DevDistricts/blob/master/LICENSE</PackageLicenseUrl>
         <PackageProjectUrl>https://github.com/akrock/DevDistricts</PackageProjectUrl>