diff --git a/source/TextBlade.Core.Tests/Characters/InventoryTests.cs b/source/TextBlade.Core.Tests/Characters/InventoryTests.cs
new file mode 100644
index 0000000..b9b0bd6
--- /dev/null
+++ b/source/TextBlade.Core.Tests/Characters/InventoryTests.cs
@@ -0,0 +1,148 @@
+using NUnit.Framework;
+using TextBlade.Core.Characters;
+
+namespace TextBlade.Core.Tests.Characters;
+
+[TestFixture]
+public class InventoryTests
+{
+    [Test]
+    [TestCase("Apple", 1, true)]
+    [TestCase("Orange", 33, true)]
+    [TestCase("Pear", 777, true)]
+    [TestCase("Banana", 0, false)]
+    public void Has_ReturnsTrue_IfItemIsInInventoryInAnyQuantity(string item, int inventoryQuantity, bool expected)
+    {
+        // Arrange
+        var inventory = new Inventory();
+        
+        for (var i = 0; i < inventoryQuantity; i++)
+        {
+            inventory.Add(item);
+        }
+
+        // Act
+        var actual = inventory.Has(item);
+
+        // Assert
+        Assert.That(actual, Is.EqualTo(expected));
+    }
+
+    [Test]
+    [TestCase(null)]
+    [TestCase("")]
+    [TestCase("             ")]
+    public void Add_Throws_IfItemIsEmpty(string itemName)
+    {
+        // Arrange
+        var inventory = new Inventory();
+
+        // Act/Assert
+        Assert.Throws<ArgumentException>(() => inventory.Add(itemName, 7));
+    }
+
+    [Test]
+    [TestCase(0)]
+    [TestCase(-1)]
+    [TestCase(-20)]
+    [TestCase(-333)]
+    public void Add_Throws_IfQuantityIsNonPositive(int quantity)
+    {
+        // Arrange
+        var inventory = new Inventory();
+
+        // Act/Assert
+        Assert.Throws<ArgumentOutOfRangeException>(() => inventory.Add("Super Awesome Item", quantity));
+    }
+
+    [Test]
+    public void Add_AddsToOrIncreasesQuantity()
+    {
+        // Arrange
+        var inventory = new Inventory();
+
+        // Act. With and without quantity; new and existing item.
+        inventory.Add("Tomato");
+        inventory.Add("Carrot", 3);
+        inventory.Add("Bell Pepper");
+        inventory.Add("Bell Pepper", 5);
+
+        // Assert
+        var actual = inventory.ItemQuantities;
+        Assert.That(actual["Tomato"], Is.EqualTo(1));
+        Assert.That(actual["Carrot"], Is.EqualTo(3));
+        Assert.That(actual["Bell Pepper"], Is.EqualTo(6));
+    }
+
+    [Test]
+    [TestCase(null)]
+    [TestCase("")]
+    [TestCase("             ")]
+    public void Remove_Throws_IfItemIsEmpty(string itemName)
+    {
+        // Arrange
+        var inventory = new Inventory();
+
+        // Act/Assert
+        Assert.Throws<ArgumentException>(() => inventory.Remove(itemName));
+    }
+
+    [Test]
+    [TestCase(0)]
+    [TestCase(-1)]
+    [TestCase(-20)]
+    [TestCase(-333)]
+    public void Remove_Throws_IfQuantityIsNonPositive(int quantity)
+    {
+        // Arrange
+        var inventory = new Inventory();
+
+        // Act/Assert
+        Assert.Throws<ArgumentOutOfRangeException>(() => inventory.Remove("Super Awesome Item", quantity));
+    }
+
+    [Test]
+    public void Remove_Throws_IfWeDontHaveTheItem()
+    {
+        // Arrange
+        var inventory = new Inventory();
+
+        // Act/Assert
+        Assert.Throws<ArgumentException>(() => inventory.Remove("Steak"));
+    }
+
+    [Test]
+    [TestCase(4)]
+    [TestCase(44)]
+    [TestCase(444)]
+    public void Remove_Throws_IfWeDontHaveTheItemInSufficientQuantities(int askQuantity)
+    {
+        // Arrange
+        var inventory = new Inventory();
+        inventory.Add("Steak", 3);
+
+        // Act/Assert
+        Assert.Throws<ArgumentOutOfRangeException>(() => inventory.Remove("Steak", askQuantity));
+    }
+
+    [Test]
+    public void Remove_DecrementsQuantity_AndRemovesItemIfQuantityBecomesZero()
+    {
+        // Arrange
+        // Arrange
+        var inventory = new Inventory();
+        inventory.Add("Fried Chicken", 3);
+        inventory.Add("French Fries", 3);
+        inventory.Add("Onion Rings", 3);
+
+        // Act
+        inventory.Remove("Fried Chicken");
+        inventory.Remove("French Fries", 2);
+        inventory.Remove("Onion Rings", 3);
+
+        // Assert.
+        Assert.That(inventory.ItemQuantities["Fried Chicken"], Is.EqualTo(2));
+        Assert.That(inventory.ItemQuantities["French Fries"], Is.EqualTo(1));
+        Assert.That(inventory.ItemQuantities.ContainsKey("Onion Rings"), Is.False);
+    }
+}
diff --git a/source/TextBlade.Core/Characters/Inventory.cs b/source/TextBlade.Core/Characters/Inventory.cs
index 23ea577..03d7ff3 100644
--- a/source/TextBlade.Core/Characters/Inventory.cs
+++ b/source/TextBlade.Core/Characters/Inventory.cs
@@ -2,7 +2,7 @@ namespace TextBlade.Core.Characters;
 
 public class Inventory
 {
-    public Dictionary<string, int> ItemQuantities = new();
+    public Dictionary<string, int> ItemQuantities { get; set; } = new();
 
     public bool Has(string item)
     {
@@ -13,12 +13,12 @@ public void Add(string item, int quantity = 1)
     {
         if (string.IsNullOrWhiteSpace(item))
         {
-            throw new ArgumentException(nameof(item));
+            throw new ArgumentException("Please specify a non-empty item", nameof(item));
         }
 
         if (quantity <= 0)
         {
-            throw new ArgumentException(nameof(quantity));
+            throw new ArgumentOutOfRangeException("Please specify a positive quantity,", nameof(quantity));
         }
         
         if (!ItemQuantities.ContainsKey(item))
@@ -33,24 +33,24 @@ public void Remove(string item, int quantity = 1)
     {
         if (string.IsNullOrWhiteSpace(item))
         {
-            throw new ArgumentException(nameof(item));
+            throw new ArgumentException("Please specify a non-empty item name", nameof(item));
         }
 
         if (quantity <= 0)
         {
-            throw new ArgumentException(nameof(quantity));
+            throw new ArgumentOutOfRangeException("Please specify a positive quantity", nameof(quantity));
         }
 
         if (!ItemQuantities.ContainsKey(item))
         {
-            throw new ArgumentException($"Can't remove {item}, we don't have any.");
+            throw new ArgumentException($"Can't remove {item}, we don't have any.", nameof(item));
         }
         else
         {
             var existingQuantity = ItemQuantities[item];
             if (existingQuantity < quantity)
             {
-                throw new ArgumentException($"Can't remove {quantity} of {item}, we only have {existingQuantity}.");
+                throw new ArgumentOutOfRangeException($"Can't remove {quantity} of {item}, we only have {existingQuantity}.", nameof(quantity));
             }
 
             ItemQuantities[item] -= quantity;
diff --git a/source/TextBlade.Core/IO/Colours.cs b/source/TextBlade.Core/IO/Colours.cs
index 608dde8..a887434 100644
--- a/source/TextBlade.Core/IO/Colours.cs
+++ b/source/TextBlade.Core/IO/Colours.cs
@@ -1,10 +1,8 @@
-using System;
-
 namespace TextBlade.Core.IO;
 
 public static class Colours
 {
-    public static string Command = "red";
-    public static string Highlight = "#00a";
+    public const string Command = "red";
+    public const string Highlight = "#00a";
 
 }