add EnumerableTests (#21978)

Co-authored-by: Edward Miller <symbiogenisis@outlook.com>

src/Core/tests/UnitTests/EnumerableExtensionTests.cs

@@ -0,0 +1,114 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using Xunit;
+
+namespace Microsoft.Maui.UnitTests
+{
+	[Category(TestCategory.Core)]
+	public partial class EnumerableExtensionTests
+	{
+		public static TheoryData<IEnumerable<int>, int, int> TestData()
+		{
+			var data = new TheoryData<IEnumerable<int>, int, int>();
+
+			var list = Enumerable.Range(0, 10).ToList();
+			var array = Enumerable.Range(0, 10).ToArray();
+			var hashSet = Enumerable.Range(0, 10).ToHashSet();
+
+			var collections = new List<IEnumerable<int>> { list, array, hashSet };
+
+			foreach (var collection in collections)
+			{
+				data.Add(collection, 99, -1);
+				data.Add(collection, 2, 2);
+			}
+
+			return data;
+		}
+
+		public static TheoryData<IEnumerable<string>, Func<string, int>, IDictionary<int, List<string>>> GroupToDictionaryData()
+		{
+			var data = new TheoryData<IEnumerable<string>, Func<string, int>, IDictionary<int, List<string>>>();
+
+			var list = new List<string> { "apple", "banana", "cherry", "date", "elderberry" };
+			var array = new string[] { "apple", "banana", "cherry", "date", "elderberry" };
+			var hashSet = new HashSet<string> { "apple", "banana", "cherry", "date", "elderberry" };
+
+			var collections = new List<IEnumerable<string>> { list, array, hashSet };
+
+			Func<string, int> func = s => s.Length;
+
+			foreach (var collection in collections)
+			{
+				var expected = collection.GroupBy(func).ToDictionary(g => g.Key, g => g.ToList());
+				data.Add(collection, func, expected);
+			}
+
+			return data;
+		}
+
+		[Fact]
+		public void ForEachDoesLoop()
+		{
+			int count = 0;
+
+			int[] array = Enumerable.Range(0, 10).ToArray();
+
+			EnumerableExtensions.ForEach(array, i => count++);
+
+			Assert.Equal(count, array.Length);
+		}
+
+		[Theory]
+		[Obsolete]
+		[MemberData(nameof(GroupToDictionaryData))]
+		public void GroupToDictionaryTest(IEnumerable<string> collection, Func<string, int> func, IDictionary<int, List<string>> expected)
+		{
+			var result = EnumerableExtensions.GroupToDictionary(collection, func);
+
+			Assert.Equal(expected, result);
+		}
+
+		[Theory]
+		[Obsolete]
+		[MemberData(nameof(TestData))]
+		public void IndexOfPredicateSucceeds(IEnumerable<int> collection, int value, int expectedIndex)
+		{
+			var index = EnumerableExtensions.IndexOf(collection, i => i == value);
+
+			Assert.Equal(expectedIndex, index);
+		}
+
+		[Theory]
+		[MemberData(nameof(TestData))]
+		public void IndexOfGenericSucceeds(IEnumerable<int> collection, int value, int expectedIndex)
+		{
+			var index = EnumerableExtensions.IndexOf(collection, value);
+
+			Assert.Equal(expectedIndex, index);
+		}
+
+		[Theory]
+		[MemberData(nameof(TestData))]
+		public void IndexOfSucceeds(IEnumerable<int> collection, int value, int expectedIndex)
+		{
+			var enumerable = collection as IEnumerable;
+
+			var index = EnumerableExtensions.IndexOf(enumerable, value);
+
+			Assert.Equal(expectedIndex, index);
+		}
+
+		[Fact]
+		public void LastSucceeds()
+		{
+			var array = Enumerable.Range(0, 10).ToArray();
+
+			var index = EnumerableExtensions.Last(array);
+
+			Assert.Equal(9, index);
+		}
+	}
+}