Add composition test for the VS implementation

src/Merq.Tests/CompositionSpec.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.ComponentModel.Composition.Primitives;
+using System.Reflection;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.ComponentModelHost;
+using Microsoft.VisualStudio.Composition;
+using Microsoft.VisualStudio.Shell;
+using Moq;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Merq;
+
+public record CompositionSpec(ITestOutputHelper Output)
+{
+    [Fact]
+    public async Task ComposeAsync()
+    {
+        // Prepare part discovery to support both flavors of MEF attributes.
+        var discovery = PartDiscovery.Combine(
+            new AttributedPartDiscovery(Resolver.DefaultInstance), // "NuGet MEF" attributes (Microsoft.Composition)
+            new AttributedPartDiscoveryV1(Resolver.DefaultInstance)); // ".NET MEF" attributes (System.ComponentModel.Composition)
+
+        // Build up a catalog of MEF parts
+        var catalog = ComposableCatalog.Create(Resolver.DefaultInstance)
+            .AddParts(await discovery.CreatePartsAsync(typeof(DefaultExportProvider).Assembly))
+            .AddPart(discovery.CreatePart(typeof(MockServiceProvider))!)
+            .AddPart(discovery.CreatePart(typeof(MockComponentModel))!);
+
+        // Assemble the parts into a valid graph.
+        var config = CompositionConfiguration.Create(catalog);
+
+        config = config.ThrowOnErrors();
+
+        // Prepare an ExportProvider factory based on this graph.
+        var epf = config.CreateExportProviderFactory();
+
+        // Create an export provider, which represents a unique container of values.
+        // You can create as many of these as you want, but typically an app needs just one.
+        var exportProvider = epf.CreateExportProvider();
+
+        var msg = exportProvider.GetExportedValue<IMessageBus>();
+
+        Assert.NotNull(msg);
+    }
+
+    [Export(typeof(SVsServiceProvider))]
+    class MockServiceProvider : SVsServiceProvider, IServiceProvider
+    {
+        public object GetService(Type serviceType)
+        {
+            if (serviceType == typeof(SVsServiceProvider))
+                return this;
+
+            if (serviceType == typeof(SComponentModel))
+                return new MockComponentModel();
+
+            var method = typeof(Mock).GetMethod(nameof(Mock.Of),
+                BindingFlags.Public | BindingFlags.Static,
+                null, Type.EmptyTypes, null)
+                .MakeGenericMethod(serviceType);
+
+            return method.Invoke(null, null);
+        }
+    }
+
+    [Export(typeof(SComponentModel))]
+    class MockComponentModel : SComponentModel, IComponentModel
+    {
+        public ComposablePartCatalog DefaultCatalog => throw new NotImplementedException();
+
+        public System.ComponentModel.Composition.Hosting.ExportProvider DefaultExportProvider => throw new NotImplementedException();
+
+        public ICompositionService DefaultCompositionService => throw new NotImplementedException();
+
+        public ComposablePartCatalog GetCatalog(string catalogName) => throw new NotImplementedException();
+        public IEnumerable<T> GetExtensions<T>() where T : class => throw new NotImplementedException();
+        public T GetService<T>() where T : class => throw new NotImplementedException();
+    }
+}

src/Merq.Tests/Merq.Tests.csproj

@@ -8,6 +8,7 @@
   <ItemGroup>
     <PackageReference Include="IsExternalInit" Version="1.0.3" PrivateAssets="all" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
+    <PackageReference Include="Microsoft.VisualStudio.Composition" Version="17.2.41" />
     <PackageReference Include="ThisAssembly.Project" Version="1.0.9" PrivateAssets="all" />
     <PackageReference Include="Moq" Version="4.18.1" />
     <PackageReference Include="xunit" Version="2.4.1" />