Add catalogitem update endpoint to public api (#418)

* Initial update endpoint working

* Updated CatalogItem to support more updates; added tests

* Got MediatR domain events working to check for duplicate item names

* Adding reference link

* Remove domain events spike code

* clean up usings

tests/UnitTests/ApplicationCore/Entities/CatalogItemTests/UpdateDetails.cs

@@ -0,0 +1,56 @@
+using Xunit;
+using Microsoft.eShopWeb.ApplicationCore.Entities;
+using System;
+
+namespace Microsoft.eShopWeb.UnitTests.ApplicationCore.Entities.CatalogItemTests
+{
+    public class UpdateDetails
+    {
+        private CatalogItem _testItem;
+        private int _validTypeId = 1;
+        private int _validBrandId = 2;
+        private string _validDescription = "test description";
+        private string _validName = "test name";
+        private decimal _validPrice = 1.23m;
+        private string _validUri = "/123";
+
+        public UpdateDetails()
+        {
+            _testItem = new CatalogItem(_validTypeId, _validBrandId, _validDescription, _validName, _validPrice, _validUri);
+        }
+
+        [Fact]
+        public void ThrowsArgumentExceptionGivenEmptyName()
+        {
+            string newValue = "";
+            Assert.Throws<ArgumentException>(() => _testItem.UpdateDetails(newValue, _validDescription, _validPrice));
+        }
+
+        [Fact]
+        public void ThrowsArgumentExceptionGivenEmptyDescription()
+        {
+            string newValue = "";
+            Assert.Throws<ArgumentException>(() => _testItem.UpdateDetails(_validName, newValue, _validPrice));
+        }
+
+        [Fact]
+        public void ThrowsArgumentNullExceptionGivenNullName()
+        {
+            Assert.Throws<ArgumentNullException>(() => _testItem.UpdateDetails(null, _validDescription, _validPrice));
+        }
+
+        [Fact]
+        public void ThrowsArgumentNullExceptionGivenNullDescription()
+        {
+            Assert.Throws<ArgumentNullException>(() => _testItem.UpdateDetails(_validName, null, _validPrice));
+        }
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(-1.23)]
+        public void ThrowsArgumentExceptionGivenNonPositivePrice(decimal newPrice)
+        {
+            Assert.Throws<ArgumentException>(() => _testItem.UpdateDetails(_validName, _validDescription, newPrice));
+        }
+    }
+}