diff --git a/csharp.xUnit/GildedRoseTests/GildedRoseTest.cs b/csharp.xUnit/GildedRoseTests/GildedRoseTest.cs
index c0c793e9..370a1b64 100644
--- a/csharp.xUnit/GildedRoseTests/GildedRoseTest.cs
+++ b/csharp.xUnit/GildedRoseTests/GildedRoseTest.cs
@@ -1,4 +1,4 @@
-using Xunit;
+using Xunit;
 using System.Collections.Generic;
 using GildedRoseKata;
 
@@ -6,12 +6,160 @@ namespace GildedRoseTests;
 
 public class GildedRoseTest
 {
+    private const string AgedBrie = "Aged Brie";
+    private const string Sulfuras = "Sulfuras, Hand of Ragnaros";
+    private const string BackstagePass = "Backstage passes to a TAFKAL80ETC concert";
+
+    private static Item UpdateOne(string name, int sellIn, int quality)
+    {
+        var item = new Item { Name = name, SellIn = sellIn, Quality = quality };
+        var app = new GildedRose(new List<Item> { item });
+        app.UpdateQuality();
+        return item;
+    }
+
     [Fact]
     public void UpdateQuality_DoesNotChangeItemName()
     {
-        IList<Item> items = new List<Item> { new Item { Name = "foo", SellIn = 0, Quality = 0 } };
-        GildedRose app = new GildedRose(items);
-        app.UpdateQuality();
-        Assert.Equal("foo", items[0].Name);
+        var item = UpdateOne("foo", 0, 0);
+        Assert.Equal("foo", item.Name);
     }
-}
\ No newline at end of file
+
+    // ---------- Normal items ----------
+
+    [Fact]
+    public void NormalItem_BeforeSellBy_QualityDropsByOne()
+    {
+        var item = UpdateOne("+5 Dexterity Vest", 10, 20);
+        Assert.Equal(9, item.SellIn);
+        Assert.Equal(19, item.Quality);
+    }
+
+    [Fact]
+    public void NormalItem_OnSellByDate_QualityDropsByTwo()
+    {
+        var item = UpdateOne("+5 Dexterity Vest", 0, 20);
+        Assert.Equal(-1, item.SellIn);
+        Assert.Equal(18, item.Quality);
+    }
+
+    [Fact]
+    public void NormalItem_AfterSellBy_QualityDropsByTwo()
+    {
+        var item = UpdateOne("+5 Dexterity Vest", -1, 20);
+        Assert.Equal(-2, item.SellIn);
+        Assert.Equal(18, item.Quality);
+    }
+
+    [Fact]
+    public void NormalItem_QualityNeverNegative()
+    {
+        var item = UpdateOne("+5 Dexterity Vest", 5, 0);
+        Assert.Equal(0, item.Quality);
+    }
+
+    [Fact]
+    public void NormalItem_AfterSellByWithQualityOne_QualityStopsAtZero()
+    {
+        var item = UpdateOne("+5 Dexterity Vest", 0, 1);
+        Assert.Equal(0, item.Quality);
+    }
+
+    // ---------- Aged Brie ----------
+
+    [Fact]
+    public void AgedBrie_BeforeSellBy_QualityIncreasesByOne()
+    {
+        var item = UpdateOne(AgedBrie, 2, 0);
+        Assert.Equal(1, item.SellIn);
+        Assert.Equal(1, item.Quality);
+    }
+
+    [Fact]
+    public void AgedBrie_AfterSellBy_QualityIncreasesByTwo()
+    {
+        var item = UpdateOne(AgedBrie, 0, 10);
+        Assert.Equal(-1, item.SellIn);
+        Assert.Equal(12, item.Quality);
+    }
+
+    [Fact]
+    public void AgedBrie_QualityNeverExceedsFifty()
+    {
+        var item = UpdateOne(AgedBrie, 5, 50);
+        Assert.Equal(50, item.Quality);
+    }
+
+    [Fact]
+    public void AgedBrie_AfterSellByAtFortyNine_QualityCapsAtFifty()
+    {
+        var item = UpdateOne(AgedBrie, 0, 49);
+        Assert.Equal(50, item.Quality);
+    }
+
+    // ---------- Sulfuras ----------
+
+    [Fact]
+    public void Sulfuras_AtSellInZero_NeverChanges()
+    {
+        var item = UpdateOne(Sulfuras, 0, 80);
+        Assert.Equal(0, item.SellIn);
+        Assert.Equal(80, item.Quality);
+    }
+
+    [Fact]
+    public void Sulfuras_AtSellInMinusOne_NeverChanges()
+    {
+        var item = UpdateOne(Sulfuras, -1, 80);
+        Assert.Equal(-1, item.SellIn);
+        Assert.Equal(80, item.Quality);
+    }
+
+    // ---------- Backstage passes ----------
+
+    [Fact]
+    public void BackstagePass_MoreThanTenDays_QualityIncreasesByOne()
+    {
+        var item = UpdateOne(BackstagePass, 11, 20);
+        Assert.Equal(10, item.SellIn);
+        Assert.Equal(21, item.Quality);
+    }
+
+    [Fact]
+    public void BackstagePass_TenDaysOrLess_QualityIncreasesByTwo()
+    {
+        var item = UpdateOne(BackstagePass, 10, 20);
+        Assert.Equal(9, item.SellIn);
+        Assert.Equal(22, item.Quality);
+    }
+
+    [Fact]
+    public void BackstagePass_SixDays_QualityIncreasesByTwo()
+    {
+        var item = UpdateOne(BackstagePass, 6, 20);
+        Assert.Equal(22, item.Quality);
+    }
+
+    [Fact]
+    public void BackstagePass_FiveDaysOrLess_QualityIncreasesByThree()
+    {
+        var item = UpdateOne(BackstagePass, 5, 20);
+        Assert.Equal(4, item.SellIn);
+        Assert.Equal(23, item.Quality);
+    }
+
+    [Fact]
+    public void BackstagePass_AfterConcert_QualityDropsToZero()
+    {
+        var item = UpdateOne(BackstagePass, 0, 20);
+        Assert.Equal(-1, item.SellIn);
+        Assert.Equal(0, item.Quality);
+    }
+
+    [Fact]
+    public void BackstagePass_AtFortyNineCloseToConcert_QualityCapsAtFifty()
+    {
+        var item = UpdateOne(BackstagePass, 5, 49);
+        Assert.Equal(50, item.Quality);
+    }
+}