porting 7.6-rc1 into 8

src/Umbraco.Tests/Collections/OrderedHashSetTests.cs

@@ -0,0 +1,81 @@
+using System;
+using NUnit.Framework;
+using Umbraco.Core;
+
+namespace Umbraco.Tests.Collections
+{
+    [TestFixture]
+    public class OrderedHashSetTests
+    {
+        [Test]
+        public void Keeps_Last()
+        {
+            var list = new OrderedHashSet<MyClass>(keepOldest: false);
+            var items = new[] { new MyClass("test"), new MyClass("test"), new MyClass("test") };
+            foreach (var item in items)
+            {
+                list.Add(item);
+            }
+
+            Assert.AreEqual(1, list.Count);
+            Assert.AreEqual(items[2].Id, list[0].Id);
+            Assert.AreNotEqual(items[0].Id, list[0].Id);
+        }
+
+        [Test]
+        public void Keeps_First()
+        {
+            var list = new OrderedHashSet<MyClass>(keepOldest: true);
+            var items = new[] { new MyClass("test"), new MyClass("test"), new MyClass("test") };
+            foreach (var item in items)
+            {
+                list.Add(item);
+            }
+
+            Assert.AreEqual(1, list.Count);
+            Assert.AreEqual(items[0].Id, list[0].Id);
+        }
+
+        private class MyClass : IEquatable<MyClass>
+        {
+            public MyClass(string name)
+            {
+                Name = name;
+                Id = Guid.NewGuid();
+            }
+
+            public string Name { get; }
+            public Guid Id { get; }
+
+            public bool Equals(MyClass other)
+            {
+                if (ReferenceEquals(null, other)) return false;
+                if (ReferenceEquals(this, other)) return true;
+                return string.Equals(Name, other.Name);
+            }
+
+            public override bool Equals(object obj)
+            {
+                if (ReferenceEquals(null, obj)) return false;
+                if (ReferenceEquals(this, obj)) return true;
+                if (obj.GetType() != this.GetType()) return false;
+                return Equals((MyClass)obj);
+            }
+
+            public override int GetHashCode()
+            {
+                return Name.GetHashCode();
+            }
+
+            public static bool operator ==(MyClass left, MyClass right)
+            {
+                return Equals(left, right);
+            }
+
+            public static bool operator !=(MyClass left, MyClass right)
+            {
+                return Equals(left, right) == false;
+            }
+        }
+    }
+}