Looking to unit test logging but blocked by extension method currently.

src/Web/Controllers/CatalogController.cs

@@ -3,10 +3,10 @@ using Microsoft.eShopWeb.ViewModels;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc;
 using System;
-using System.IO;
 using System.Threading.Tasks;
 using ApplicationCore.Interfaces;
 using ApplicationCore.Exceptions;
+using Microsoft.Extensions.Logging;
 
 namespace Microsoft.eShopWeb.Controllers
 {
@@ -15,17 +15,19 @@ namespace Microsoft.eShopWeb.Controllers
         private readonly IHostingEnvironment _env;
         private readonly ICatalogService _catalogService;
         private readonly IImageService _imageService;
+        private readonly ILogger<CatalogController> _logger;
 
         public CatalogController(IHostingEnvironment env,
             ICatalogService catalogService,
-            IImageService imageService)
+            IImageService imageService,
+            ILogger<CatalogController> logger)
         {
             _env = env;
             _catalogService = catalogService;
             _imageService = imageService;
+            _logger = logger;
         }
 
-
         // GET: /<controller>/
         public async Task<IActionResult> Index(int? BrandFilterApplied, int? TypesFilterApplied, int? page)
         {
@@ -66,6 +68,7 @@ namespace Microsoft.eShopWeb.Controllers
             }
             catch (CatalogImageMissingException ex)
             {
+                _logger.LogWarning($"No image found for id: {id}");
                 return NotFound();
             }
             return File(imageBytes, "image/png");

tests/UnitTests/Web/Controllers/CatalogControllerGetImage.cs

@@ -3,6 +3,7 @@ using ApplicationCore.Interfaces;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.eShopWeb.Controllers;
+using Microsoft.Extensions.Logging;
 using Moq;
 using Xunit;
 
@@ -11,22 +12,21 @@ namespace UnitTests
     public class CatalogControllerGetImage
     {
         private Mock<IImageService> _mockImageService = new Mock<IImageService>();
+        private Mock<ILogger<CatalogController>> _mockLogger = new Mock<ILogger<CatalogController>>();
         private CatalogController _controller;
         private int _testImageId = 123;
         private byte[] _testBytes = { 0x01, 0x02, 0x03 };
 
         public CatalogControllerGetImage()
         {
-            _controller = new CatalogController(null, null, _mockImageService.Object);
+            _controller = new CatalogController(null, null, _mockImageService.Object,
+                _mockLogger.Object);
         }
 
         [Fact]
         public void CallsImageServiceWithId()
         {
-            _mockImageService
+            SetupImageWithTestBytes();
-                .Setup(i => i.GetImageBytesById(_testImageId))
-                .Returns(_testBytes)
-                .Verifiable();
 
             _controller.GetImage(_testImageId);
             _mockImageService.Verify();
@@ -35,9 +35,7 @@ namespace UnitTests
         [Fact]
         public void ReturnsFileResultWithBytesGivenSuccess()
         {
-            _mockImageService
+            SetupImageWithTestBytes();
-                .Setup(i => i.GetImageBytesById(_testImageId))
-                .Returns(_testBytes);
 
             var result = _controller.GetImage(_testImageId);
 
@@ -48,13 +46,38 @@ namespace UnitTests
         [Fact]
         public void ReturnsNotFoundResultGivenImageMissingException()
         {
-            _mockImageService
+            SetupMissingImage();
-                .Setup(i => i.GetImageBytesById(_testImageId))
-                .Throws(new CatalogImageMissingException("missing image"));
 
             var result = _controller.GetImage(_testImageId);
 
             var actionResult = Assert.IsType<NotFoundResult>(result);
         }
+
+        [Fact]
+        public void LogsWarningGivenImageMissingException()
+        {
+            SetupMissingImage();
+            _mockLogger.Setup(l => l.LogWarning(It.IsAny<string>()))
+                .Verifiable();
+
+            _controller.GetImage(_testImageId);
+
+            _mockLogger.Verify();
+        }
+
+        private void SetupMissingImage()
+        {
+            _mockImageService
+                .Setup(i => i.GetImageBytesById(_testImageId))
+                .Throws(new CatalogImageMissingException("missing image"));
+        }
+
+        private void SetupImageWithTestBytes()
+        {
+            _mockImageService
+                .Setup(i => i.GetImageBytesById(_testImageId))
+                .Returns(_testBytes)
+                .Verifiable();
+        }
     }
 }