Test badly formed container

src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/ActivatorUtilitiesTests.cs

@@ -378,6 +378,26 @@ public void GetServiceOrCreateInstanceUnregisteredService()
             }
         }
 
+        [Fact]
+        public void CreateInstance_BadlyConfiguredIServiceProviderIsService_ProperlyCreatesUnambiguousInstance()
+        {
+            if (SupportsIServiceProviderIsService)
+            {
+                return;
+            }
+
+            var serviceCollection = new TestServiceCollection()
+                .AddScoped<FakeService1>();
+            var fakeIServiceProviderIsService = new FakeIServiceProviderIsService();
+
+            serviceCollection.AddScoped<IServiceProviderIsService>((p) => (IServiceProviderIsService)fakeIServiceProviderIsService);
+            var serviceProvider = CreateServiceProvider(serviceCollection);
+
+            var instance = ActivatorUtilities.CreateInstance<FakeService2>(serviceProvider);
+            Assert.NotNull(instance);
+            Assert.True(fakeIServiceProviderIsService.Called);
+        }
+
         [Theory]
         [MemberData(nameof(CreateInstanceFuncs))]
         public void CreateInstance_NullInstance_HandlesBadInputWithInvalidOperationException(CreateInstanceFunc createFunc)
@@ -431,6 +451,16 @@ public void CreateInstance_CapturesInnerException_OfTargetInvocationException()
             Assert.Equal(msg, ex.Message);
         }
 
+        private class FakeIServiceProviderIsService : IServiceProviderIsService
+        {
+            public FakeIServiceProviderIsService() { }
+            public bool Called { get; set; }
+            public bool IsService(Type serviceType) { Called = true; return false; }
+        }
+
+        private class FakeService1 { public FakeService1() { } }
+        private class FakeService2 { public FakeService2(FakeService1 fakeService) { } }
+
         private abstract class AbstractFoo
         {
             // The constructor should be public, since that is checked as well.