Add mini unit test

Author: Forgind

src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenADependencyContextBuilder.cs

@@ -195,6 +195,15 @@ public void ItDoesntCreateReferenceAssembliesWhenNoCompilationOptions()
                 .NotContain(d => d.Name == "System.Collections.NonGeneric.Reference");
         }
 
+        [Fact]
+        public void ItDoesntCreateKeepUnneededRuntimeReferences()
+        {
+            DependencyContext dependencyContext = BuildDependencyContextWithReferenceAssemblies(useCompilationOptions: false);
+
+            dependencyContext.RuntimeLibraries.Count.Should().Be(1);
+            dependencyContext.RuntimeLibraries[0].Name.Should().Be("simple.dependencies"); // This is the entrypoint
+        }
+
         [Fact]
         public void ItHandlesReferenceAndPackageReferenceNameCollisions()
         {