Add file upload model binding integration tests (#444)

* Initial plan

* Add file upload model binding integration tests

Co-authored-by: gunndabad <2041280+gunndabad@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: gunndabad <2041280+gunndabad@users.noreply.github.com>

Author: Copilot

tests/GovUk.Frontend.AspNetCore.IntegrationTests/TagHelperModelBindingTests/FileUpload.cshtml

@@ -0,0 +1,3 @@
+@model GovUk.Frontend.AspNetCore.IntegrationTests.TagHelperModelBindingTests.FileUploadTestsModel
+
+<govuk-file-upload for="File" />

tests/GovUk.Frontend.AspNetCore.IntegrationTests/TagHelperModelBindingTests/FileUploadOverridden.cshtml

@@ -0,0 +1,7 @@
+@model GovUk.Frontend.AspNetCore.IntegrationTests.TagHelperModelBindingTests.FileUploadTestsModel
+
+<govuk-file-upload for="File" name="OverriddenName" id="OverriddenId">
+    <govuk-file-upload-label>Overridden label</govuk-file-upload-label>
+    <govuk-file-upload-hint>Overridden hint</govuk-file-upload-hint>
+    <govuk-file-upload-error-message>Overridden error message</govuk-file-upload-error-message>
+</govuk-file-upload>

tests/GovUk.Frontend.AspNetCore.IntegrationTests/TagHelperModelBindingTests/Tests.cs

@@ -261,6 +261,48 @@ public async Task CharacterCountOverridden_RendersCorrectly()
         var errorMessage = page.Locator(".govuk-error-message").First;
         Assert.Equal("Error: Overridden error message", await errorMessage.TextContentAsync());
     }
+
+    [Fact]
+    public async Task FileUpload_RendersCorrectly()
+    {
+        var page = await fixture.Browser!.NewPageAsync();
+        await page.GotoAsync($"{ServerFixture.BaseUrl}/ModelBindingTests/FileUpload");
+
+        var input = page.Locator("input[type='file']").First;
+        Assert.Equal("File", await input.GetAttributeAsync("name"));
+        Assert.Equal("File", await input.GetAttributeAsync("id"));
+
+        var label = page.Locator("label").First;
+        Assert.Equal("File", await label.GetAttributeAsync("for"));
+        Assert.Equal("ModelMetadata display name", await label.InnerTextAsync());
+
+        var hint = page.Locator(".govuk-hint").First;
+        Assert.Equal("ModelMetadata description", await hint.InnerTextAsync());
+
+        var errorMessage = page.Locator(".govuk-error-message").First;
+        Assert.Equal("Error: Model error message", await errorMessage.TextContentAsync());
+    }
+
+    [Fact]
+    public async Task FileUploadOverridden_RendersCorrectly()
+    {
+        var page = await fixture.Browser!.NewPageAsync();
+        await page.GotoAsync($"{ServerFixture.BaseUrl}/ModelBindingTests/FileUploadOverridden");
+
+        var input = page.Locator("input[type='file']").First;
+        Assert.Equal("OverriddenName", await input.GetAttributeAsync("name"));
+        Assert.Equal("OverriddenId", await input.GetAttributeAsync("id"));
+
+        var label = page.Locator("label").First;
+        Assert.Equal("OverriddenId", await label.GetAttributeAsync("for"));
+        Assert.Equal("Overridden label", await label.InnerTextAsync());
+
+        var hint = page.Locator(".govuk-hint").First;
+        Assert.Equal("Overridden hint", await hint.InnerTextAsync());
+
+        var errorMessage = page.Locator(".govuk-error-message").First;
+        Assert.Equal("Error: Overridden error message", await errorMessage.TextContentAsync());
+    }
 }
 
 [Route("/[controller]/[action]")]
@@ -342,6 +384,20 @@ public IActionResult CharacterCountOverridden()
         ModelState.AddModelError(nameof(CharacterCountTestsModel.Text), "Model error message");
         return View(new CharacterCountTestsModel { Text = "Model value" });
     }
+
+    [HttpGet]
+    public IActionResult FileUpload()
+    {
+        ModelState.AddModelError(nameof(FileUploadTestsModel.File), "Model error message");
+        return View(new FileUploadTestsModel());
+    }
+
+    [HttpGet]
+    public IActionResult FileUploadOverridden()
+    {
+        ModelState.AddModelError(nameof(FileUploadTestsModel.File), "Model error message");
+        return View(new FileUploadTestsModel());
+    }
 }
 
 public record TextInputTestsModel
@@ -373,3 +429,9 @@ public record CharacterCountTestsModel
     [Display(Name = "ModelMetadata display name", Description = "ModelMetadata description")]
     public string? Text { get; set; }
 }
+
+public record FileUploadTestsModel
+{
+    [Display(Name = "ModelMetadata display name", Description = "ModelMetadata description")]
+    public Microsoft.AspNetCore.Http.IFormFile? File { get; set; }
+}