Add metapackage test

Author: stan-sz

src/Tests/E2ETests.cs

@@ -318,6 +318,14 @@ public Task UnusedPackageReferenceWithSdk()
             ]);
     }
 
+    [TestMethod]
+    public Task UnusedPackageReferenceWithMetaPackage()
+    {
+        return RunMSBuildAsync(
+            projectFile: "Test/Test.csproj",
+            expectedWarnings: []);
+    }
+
     [TestMethod]
     public Task UnusedPackageReferenceNoWarn()
     {

src/Tests/TestData/UnusedPackageReferenceWithMetaPackage/Test/Test.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Frozen;
+
+namespace Test
+{
+    public class Foo
+    {
+        public static FrozenSet<int> SomeSet() => FrozenSet.ToFrozenSet(Array.Empty<int>());
+    }
+}

src/Tests/TestData/UnusedPackageReferenceWithMetaPackage/Test/Test.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="MSTest.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ExplicitUsings>enable</ExplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MSTest" Version="4.1.0" />
+  </ItemGroup>
+
+</Project>