Ease unit testing of `Controller.TryValidateModel()`

- #3586
- reverse conditions to access `_options.Value` only when test has set up an `IStringLocalizerFactory`

src/Microsoft.AspNet.Mvc.DataAnnotations/DataAnnotationsModelValidatorProvider.cs

@@ -2,7 +2,9 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.ComponentModel.DataAnnotations;
+#if DOTNET5_4
 using System.Reflection;
+#endif
 using Microsoft.Extensions.Localization;
 using Microsoft.Extensions.OptionsModel;
 
@@ -34,7 +36,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Validation
         public void GetValidators(ModelValidatorProviderContext context)
         {
             IStringLocalizer stringLocalizer = null;
-            if (_options.Value.DataAnnotationLocalizerProvider != null && _stringLocalizerFactory != null)
+            if (_stringLocalizerFactory != null && _options.Value.DataAnnotationLocalizerProvider != null)
             {
                 stringLocalizer = _options.Value.DataAnnotationLocalizerProvider(
                     context.ModelMetadata.ContainerType ?? context.ModelMetadata.ModelType,

test/Microsoft.AspNet.Mvc.ViewFeatures.Test/ControllerTest.cs

@@ -1770,6 +1770,22 @@ namespace Microsoft.AspNet.Mvc.Test
             Assert.Equal("Out of range!", error.ErrorMessage);
         }
 
+        [Fact]
+        public void TryValidateModel_Succeeds_WithoutValidatorMetadata()
+        {
+            // Arrange
+            // Do not add a Mock validator provider to this test. Test is intended to demonstrate ease of unit testing
+            // and exercise DataAnnotationsModelValidatorProvider, avoiding #3586 regressions.
+            var model = new TryValidateModelModel();
+            var controller = GetController(binder: null, provider: null);
+
+            // Act
+            var result = controller.TryValidateModel(model);
+
+            // Assert
+            Assert.True(controller.ModelState.IsValid);
+        }
+
         [Fact]
         public void TryValidateModelEmptyBindingContextThrowsException()
         {