diff --git a/LinqStudy.Test/LinqToObject/SetsTest.cs b/LinqStudy.Test/LinqToObject/SetsTest.cs
new file mode 100644
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+++ b/LinqStudy.Test/LinqToObject/SetsTest.cs
@@ -0,0 +1,226 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using Xunit;
+
+namespace LinqStudy.Test.LinqToObject
+{
+    /// <summary>
+    /// Sets 集合操作符
+    /// 注意：集合操作为 “延迟执行”，数据源为null时均引发异常。
+    /// </summary>
+    public class SetsTest
+    {
+        #region Distinct
+
+        /// <summary>
+        /// Distinct：元素去重;延迟执行。
+        /// 注意：值类型可以直接去重；引用类型比较的是引用而不是对象本身的属性等，可以提供自定义比较器。
+        /// </summary>
+        [Fact]
+        public void Distinct_Test()
+        {
+            List<int> array = new List<int>() { 1, 2, 2, 3, 3, 3 };
+
+            var distinctItem = array.Distinct();
+            var expected = new List<int>() { 1, 2, 3 };
+
+            Assert.Equal(expected, distinctItem);
+        }
+
+        /// <summary>
+        /// 引用类型：剔除同一个引用的重复项。
+        /// </summary>
+        [Fact]
+        public void Distinct_Reference_Yes_Test()
+        {
+            var p1 = new Person() { Id = 2, Name = "小龙女", Age = 28 };
+            var p2 = new Person() { Id = 4, Name = "杨过", Age = 32 };
+
+            List<Person> peoples = new List<Person>();
+            peoples.Add(p1);
+            peoples.Add(p2);
+
+            //添加对同一对象的多次引用
+            peoples.Add(p1);
+            peoples.Add(p2);
+
+            var totalCount = peoples.Count();
+            var distinctCount = peoples.Distinct().Count();
+
+            Assert.Equal(4, totalCount);
+            Assert.Equal(2, distinctCount);
+        }
+
+        [Fact]
+        public void Distinct_Reference_No_Test()
+        {
+
+            List<Person> peoples = new List<Person>()
+            {
+                new Person() { Id = 1, Name = "小龙女", Age = 28 },
+                new Person() { Id = 1, Name = "小龙女", Age = 28 },
+            };
+
+            //虽然1、2两项对象属性完命相同，但是两个不同的对象(new两次)，所以不是“重复项”
+            //去重后仍然是2项
+            var distinctCount = peoples.Distinct().Count();
+
+            Assert.Equal(2, distinctCount);
+        }
+
+        /// <summary>
+        /// 延迟执行
+        /// </summary>
+        [Fact]
+        public void Distinct_Daley_Test()
+        {
+            List<int> array = new List<int>() { 1, 2, 2, 3, 3, 3 };
+
+            var distinctItem = array.Distinct();
+
+            array.Add(5);
+
+            var expected = new List<int>() { 1, 2, 3, 5 };
+
+            Assert.Equal(expected, distinctItem);
+        }
+
+        /// <summary>
+        /// 重载：自定义比较器
+        /// </summary>
+        [Fact]
+        public void Distinct_compare_Test()
+        {
+            List<Person> peoples = new List<Person>()
+            {
+                new Person(){ Id=1, Name="小龙女", Age=28},
+                new Person(){ Id=1, Name="我不是龙女", Age=68},
+            };
+
+            var distinctItem = peoples.Distinct(new PersonEqualityComparerById());
+
+            //虽然两项只有Id属性相等，其它属性均不同；
+            //但是因为自定义比较器内部，只比较Id即只要Id相同就认为同一对象。
+            //所以去重后，只有一项(第一项，第二项被认为是重复项，被去除)。
+            var distinctCount = distinctItem.Count();
+
+            var expected = 1;
+            Assert.Equal(expected, distinctCount);
+        }
+        #endregion
+
+        #region Union
+
+        ///<summary>
+        /// Union:取两个序列的并集，并去除重复项。
+        /// 与SQL比较相似；Concat不去除重复项。
+        ///</summary>
+        [Fact]
+        public void Union_Test()
+        {
+            var p1 = new Person() { Id = 1, Name = "杨过", Age = 32 };
+            var p2 = new Person() { Id = 2, Name = "小龙女", Age = 28 };
+            var p3 = new Person() { Id = 3, Name = "银花公主", Age = 16 };
+
+            List<Person> peoples1 = new List<Person>()
+            {
+                p1,
+                p2,
+            };
+            List<Person> peoples2 = new List<Person>()
+            {
+                p1,
+                p3,
+            };
+
+            var act = peoples1.Union(peoples2);
+
+            //因为"杨过"是重复的，所有总共有3项
+            var totalCount = act.Count();
+
+            Assert.Equal(3, totalCount);
+        }
+
+        ///<summary>
+        /// Union: 对同一数据源两次查询后，两次结果Union
+        /// 注意：同一数据源多次查询形成的序列项，均是对同一对象的引用。
+        ///      项里保存的是引用地址，非对象本身。
+        ///</summary>
+        [Fact]
+        public void Union_UseQuery_Test()
+        {
+            List<Person> peoples = new List<Person>()
+            {
+                new Person(){ Id=1, Name="张三丰", Age=230},
+                new Person(){ Id=2, Name="小龙女", Age=28},
+                new Person(){ Id=3, Name="银花公主", Age=16},
+                new Person(){ Id=4, Name="杨过", Age=32},
+            };
+
+            var peoples1 = peoples.Where(q => q.Id <= 3);
+            var peoples2 = peoples.Where(q => q.Age < 230);
+
+            var act = peoples1.Union(peoples2);
+
+            //前3项 + 后3项- 重复2项=4项
+            var totalCount = act.Count();
+
+            Assert.Equal(4, totalCount);
+        }
+
+        ///<summary>
+        /// Union重载: camparer
+        ///</summary>
+        [Fact]
+        public void Union_camparer_Test()
+        {
+            var p1 = new Person() { Id = 1, Name = "杨过", Age = 32 };
+            var p2 = new Person() { Id = 2, Name = "小龙女", Age = 28 };
+            var p3 = new Person() { Id = 2, Name = "我非龙女", Age = 77 };
+
+            List<Person> peoples1 = new List<Person>()
+            {
+                p1,
+                p2,
+            };
+            List<Person> peoples2 = new List<Person>()
+            {
+                p1,
+                p3,
+            };
+
+            var act = peoples1.Union
+            (
+                peoples2,
+                new PersonEqualityComparerById()
+            )
+            .ToList();
+
+            //虽然P2和p3只有Id相同，其它不同；但自定义比较只看Id，所以P2和p3被认为是同一个对象。
+            //结果集为：p1+p2
+            var totalCount = act.Count();
+
+            Assert.Equal(2, totalCount);
+        }
+
+        ///<summary>
+        /// 异常：ArgumentNullException
+        ///</summary>
+        [Fact]
+        public void Union_ArgumentNullException_Test()
+        {
+            List<Person> peoples1 = null;
+            List<Person> peoples2 = null;
+
+            Action act = () => peoples1.Union
+             (
+                 peoples2
+             );
+
+            Assert.Throws<ArgumentNullException>(act);
+        }
+        #endregion
+    }
+}
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