Created tests that show the collections contains methods work

LiteDB.Tests/Database/Contains_Tests.cs

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+using LiteDB;
+using FluentAssertions;
+using Xunit;
+using System.IO;
+using System.Linq;
+using System.Collections.Generic;
+using System;
+
+namespace LiteDB.Tests.Database
+{
+    public class Contains_Tests
+    {
+        [Fact]
+        public void ArrayContains_ShouldHaveCount1()
+        {
+            var random = new Random();
+            var randomValue = random.Next();
+
+            using(var database = new LiteDatabase(new MemoryStream()))
+            {
+                var collection = database.GetCollection<ItemWithEnumerable>();
+                collection.Insert(new ItemWithEnumerable
+                {
+                    Array = new int[] { randomValue }
+                });
+
+                var result = collection.Find(i => i.Array.Contains(randomValue)).ToList();
+                result.Should().HaveCount(1);
+            }
+        }
+
+        [Fact]
+        public void EnumerableAssignedArrayContains_ShouldHaveCount1()
+        {
+            var random = new Random();
+            var randomValue = random.Next();
+
+            using(var database = new LiteDatabase(new MemoryStream()))
+            {
+                var collection = database.GetCollection<ItemWithEnumerable>();
+                collection.Insert(new ItemWithEnumerable
+                {
+                    Enumerable = new int[] { randomValue }
+                });
+
+                var result = collection.Find(i => i.Enumerable.Contains(randomValue)).ToList();
+                result.Should().HaveCount(1);
+            }
+        }
+
+        [Fact]
+        public void EnumerableAssignedListContains_ShouldHaveCount1()
+        {
+            var random = new Random();
+            var randomValue = random.Next();
+
+            using(var database = new LiteDatabase(new MemoryStream()))
+            {
+                var collection = database.GetCollection<ItemWithEnumerable>();
+                collection.Insert(new ItemWithEnumerable
+                {
+                    Enumerable = new List<int> { randomValue }
+                });
+
+                var result = collection.Find(i => i.Enumerable.Contains(randomValue)).ToList();
+                result.Should().HaveCount(1);
+            }
+        }
+
+        [Fact]
+        public void ListContains_ShouldHaveCount1()
+        {
+            var random = new Random();
+            var randomValue = random.Next();
+
+            using(var database = new LiteDatabase(new MemoryStream()))
+            {
+                var collection = database.GetCollection<ItemWithEnumerable>();
+                collection.Insert(new ItemWithEnumerable
+                {
+                    List = new List<int> { randomValue }
+                });
+
+                var result = collection.Find(i => i.List.Contains(randomValue)).ToList();
+                result.Should().HaveCount(1);
+            }
+        }
+
+        public class ItemWithEnumerable
+        {
+            public int[] Array { get; set; }
+            public IEnumerable<int> Enumerable { get; set; }
+            public IList<int> List { get; set; }
+        }
+    }
+}