Cherry-pick @pranavkm's functional test for #7562

- 30a5eda508 / origin/prkrishn/form-file-value-provider

Was:
Design: Use a value provider to allow nested form files

Fixes https://github.com/aspnet/Mvc/issues/7562

test/Microsoft.AspNetCore.Mvc.FunctionalTests/RazorPagesWithBasePathTest.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Net;
 using System.Net.Http;
+using System.Net.Http.Headers;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -623,6 +624,41 @@ Hello from /Pages/Shared/";
             Assert.Equal("Value from Page", valueSetInPage);
         }
 
+        [Fact]
+        public async Task RoundTrippingFormFileInputWorks()
+        {
+            // Arrange
+            var url = "/PropertyBinding/BindFormFile";
+            var response = await Client.GetAsync(url);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
+
+            var document = await response.GetHtmlDocumentAsync();
+
+            var property1 = document.RequiredQuerySelector("#property1").GetAttribute("name");
+            var file1 = document.RequiredQuerySelector("#file1").GetAttribute("name");
+            var file2 = document.RequiredQuerySelector("#file2").GetAttribute("name");
+            var file3 = document.RequiredQuerySelector("#file3").GetAttribute("name");
+            var antiforgeryToken = document.RetrieveAntiforgeryToken();
+
+            var cookie = AntiforgeryTestHelper.RetrieveAntiforgeryCookie(response);
+
+            var content = new MultipartFormDataContent();
+            content.Add(new StringContent("property1-value"), property1);
+            content.Add(new StringContent("test-value1"), file1, "test1.txt");
+            content.Add(new StringContent("test-value2"), file3, "test2.txt");
+
+            var request = new HttpRequestMessage(HttpMethod.Post, url)
+            {
+                Content = content,
+            };
+            request.Headers.Add("Cookie", cookie.Key + "=" + cookie.Value);
+            request.Headers.Add("RequestVerificationToken", antiforgeryToken);
+
+            response = await Client.SendAsync(request);
+
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
+        }
+
         private async Task AddAntiforgeryHeadersAsync(HttpRequestMessage request)
         {
             var response = await Client.GetAsync(request.RequestUri);

test/WebSites/RazorPagesWebSite/Pages/PropertyBinding/BindFormFile.cshtml

@@ -0,0 +1,10 @@
+@page
+@model BindFormFile
+@addTagHelper "*, Microsoft.AspNetCore.Mvc.TagHelpers"
+
+<form method="post" enctype="multipart/form-data">
+    <input id="property1" asp-for="Property1" />
+    <input id="file1" asp-for="Forms.Form1" />
+    <input id="file2" asp-for="Forms.Form2" />
+    <input id="file3" asp-for="Form3" />
+</form>

test/WebSites/RazorPagesWebSite/Pages/PropertyBinding/BindFormFile.cshtml.cs

@@ -0,0 +1,52 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace RazorPagesWebSite
+{
+    [BindProperties]
+    public class BindFormFile : PageModel
+    {
+        public string Property1 { get; set; }
+
+        public IFormFile Form3 { get; set; }
+
+        public FormFiles Forms { get; set; }
+
+        public IActionResult OnPost()
+        {
+            if (string.IsNullOrEmpty(Property1))
+            {
+                throw new Exception($"{nameof(Property1)} is not bound.");
+            }
+
+            if (string.IsNullOrEmpty(Form3.Name) || Form3.Length == 0)
+            {
+                throw new Exception($"{nameof(Form3)} is not bound.");
+            }
+
+            if (string.IsNullOrEmpty(Forms.Form1.Name) || Forms.Form1.Length == 0)
+            {
+                throw new Exception($"{nameof(Forms.Form1)} is not bound.");
+            }
+
+            if (Forms.Form2 != null)
+            {
+                throw new Exception($"{nameof(Forms.Form2)} is bound.");
+            }
+
+            return new OkResult();
+        }
+    }
+
+    public class FormFiles
+    {
+        public IFormFile Form1 { get; set; }
+
+        public IFormFile Form2 { get; set; }
+    }
+}