mono/mcs/class/System.Core/Test/System.Linq/EnumerableFixture.cs

#region License, Terms and Author(s)
//
// BackLINQ
// Copyright (c) 2008 Atif Aziz. All rights reserved.
//
//  Author(s):
//
//      Dominik Hug, http://www.dominikhug.ch
//
// This library is free software; you can redistribute it and/or modify it
// under the terms of the New BSD License, a copy of which should have
// been delivered along with this distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
#endregion

using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
using System.Threading;
using NUnit.Framework;
using System.Linq;
using NUnit.Framework.SyntaxHelpers;
using NUnit.Framework.Constraints;
using System.Diagnostics;

namespace MonoTests.System.Linq {
	[TestFixture]
	public sealed class EnumerableFixture {
		private CultureInfo initialCulture; // Thread culture saved during Setup to be undone in TearDown.
		private AssertionHandler tearDownAssertions;

		private delegate void AssertionHandler ();

		[SetUp]
		public void SetUp ()
		{
			tearDownAssertions = null;
			initialCulture = Thread.CurrentThread.CurrentCulture;
			Thread.CurrentThread.CurrentCulture = new CultureInfo ("de-CH");
		}

		[TearDown]
		public void TearDown ()
		{
			if (tearDownAssertions != null)
				tearDownAssertions ();
			Thread.CurrentThread.CurrentCulture = initialCulture;
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Aggregate_EmptySource_ThrowsInvalidOperationException ()
		{
			var source = Read<object> ();
			source.Aggregate ((a, b) => { throw new NotImplementedException (); });
		}

		[Test]
		public void Aggregate_AddFuncOnIntegers_ReturnsTotal ()
		{
			var source = Read (new [] { 12, 34, 56, 78, 910, 1112, 1314, 1516, 1718, 1920 });
			var result = source.Aggregate ((a, b) => a + b);
			Assert.That (result, Is.EqualTo (8670));
		}

		[Test]
		public void Aggregate_AddFuncOnIntegersWithSeed_ReturnsTotal ()
		{
			var source = Read (new [] { 12, 34, 56, 78, 910, 1112, 1314, 1516, 1718, 1920 });
			var result = source.Aggregate (100, (a, b) => a + b);
			Assert.That (result, Is.EqualTo (8770));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Aggregate_NullSource_ThrowsArgumentNullException ()
		{
			Enumerable.Aggregate<object> (null, (a, e) => { throw new NotImplementedException (); });
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Aggregate_NullFunc_ThrowsArgumentNullException ()
		{
			Read<object> ().Aggregate (null);
		}

		[Test]
		public void Empty_YieldsEmptySource ()
		{
			var source = Enumerable.Empty<String> ();
			Assert.That (source, Is.Not.Null);
			var e = source.GetEnumerator ();
			Assert.That (e, Is.Not.Null);
			Assert.That (e.MoveNext (), Is.False);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Cast_NullSource_ThrowsArgumentNullException ()
		{
			Enumerable.Cast<object> (null);
		}

		[Test]
		[ExpectedException (typeof (InvalidCastException))]
		public void Cast_InvalidSource_ThrowsInvalidCastException ()
		{
			var source = Read (new object [] { 1000, "hello", new object () });
			var target = source.Cast<byte> ();
			// do something with the results so Cast will really be executed (deferred execution)
			var sb = new StringBuilder ();
			foreach (var b in target) {
				sb.Append (b.ToString ());
			}
		}

		[Test]
		public void Cast_ObjectSourceContainingIntegers_YieldsDowncastedIntegers ()
		{
			var source = Read (new object [] { 1, 10, 100 });
			source.Cast<int> ().AssertEquals (1, 10, 100);
		}

		[Test]
		public void Cast_Integers_YieldsUpcastedObjects ()
		{
			Read (new [] { 1, 10, 100 }).Cast<object> ().AssertEquals (1, 10, 100);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void All_NullSource_ThrowsArgumentNullException ()
		{
			Enumerable.All (null, (int i) => { throw new NotImplementedException (); });
		}

		[Test]
		public void All_SomeSourceElementsNotSatifyingPredicate_ReturnsFalse ()
		{
			var source = Read (new [] { -100, -1, 0, 1, 100 });
			Assert.That (source.All (i => i >= 0), Is.False);
		}

		[Test]
		public void All_SourceElementsSatisfyingPredicate_ReturnsTrue ()
		{
			var source = Read (new [] { -100, -1, 0, 1, 100 });
			Assert.That (source.All (i => i >= -100), Is.True);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Any_NullSource_ThrowsArgumentNullException ()
		{
			Enumerable.Any<object> (null);
		}

		[Test]
		public void Any_EmptySource_ReturnsFalse ()
		{
			var source = Read<object> ();
			Assert.That (source.Any (), Is.False);
		}

		[Test]
		public void Any_NonEmptySource_ReturnsTrue ()
		{
			var source = Read (new [] { new object () });
			Assert.That (source.Any (), Is.True);
		}

		[Test]
		public void Any_PredicateArg_EmptySource_ReturnsFalse ()
		{
			var source = Read (new int [0]);
			Assert.That (source.Any (i => { throw new NotImplementedException (); }), Is.False);
		}

		[Test]
		public void Any_PredicateArg_NonEmptySource_ReturnsTrue ()
		{
			Assert.That (Read (new [] { 100 }).Any (i => i > 0), Is.True);
		}

		[Test]
		public void Average_Longs_ReturnsAverage ()
		{
			Assert.That (Read (new [] { 25L, 75L }).Average (), Is.EqualTo (50));
		}

		[Test]
		public void Average_NullableLongs_ReturnsAverage ()
		{
			Assert.That (Read (new long? [] { 12L, 34L, null, 56L }).Average (), Is.EqualTo (34.0));
		}

		[Test]
		public void Average_NullableInts_ReturnsAverage ()
		{
			Assert.That (Read (new int? [] { 12, 34, null, 56 }).Average (), Is.EqualTo (34.0));
		}

		[Test]
		public void Average_Decimals_ReturnsToleratableAverage ()
		{
			var source = Read (new [] { -10000m, 2.0001m, 50m });
			Assert.That (source.Average (), Is.EqualTo (-3315.999966).Within (0.00001));
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Average_EmptySource_ThrowsInvalidOperationException ()
		{
			Read<int> ().Average ();
		}

		[Test]
		public void Average_EmptyArrayOfNullableIntegers_ReturnsNull ()
		{
			Assert.That (Read<int?> ().Average (), Is.Null);
		}

		[Test]
		public void Average_Selector_ArrayOfPersons_AverageAge ()
		{
			var source = Read (Person.CreatePersons ());
			Assert.That (source.Average (p => p.Age).Equals (22.5));
		}

		[Test]
		public void Average_ArrayOfDoubles_ReturnsAverage ()
		{
			var source = Read (new [] { -3.45, 9.001, 10000.01 });
			Assert.That (source.Average (), Is.EqualTo (3335.187).Within (0.01));
		}

		[Test]
		public void Average_ArrayOfFloats_ReturnsAverage ()
		{
			var source = Read (new [] { -3.45F, 9.001F, 10000.01F });
			Assert.That (source.Average (), Is.EqualTo (3335.187).Within (0.01));
		}

		[Test]
		public void Average_ArrayOfNullableFloats_ReturnsAverage ()
		{
			var source = Read (new float? [] { -3.45F, 9.001F, 10000.01F, null });
			Assert.That (source.Average (), Is.EqualTo (3335.187).Within (0.01));
		}

		[Test]
		public void Average_NullableDoubles_ReturnsAverage ()
		{
			var source = Read (new double? [] { -3.45, 9.001, 10000.01, null });
			Assert.That (source.Average (), Is.EqualTo (3335.187).Within (0.01));
		}

		[Test]
		public void Average_NullableDecimals_ReturnsAverage ()
		{
			var source = Read (new decimal? [] { -3.45m, 9.001m, 10000.01m, null });
			Assert.That (source.Average (), Is.EqualTo (3335.187).Within (0.01));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Concat_FirstSourceNull_ThrowsArgumentNullException ()
		{
			Enumerable.Concat (null, new object [0]);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Concat_SecondSourceNull_ThrowsArgumentNullException ()
		{
			new object [0].Concat (null);
		}

		[Test]
		public void Concat_TwoLists_CorrectOrder ()
		{
			var first = Read (new [] { 12, 34, 56 });
			var second = Read (new [] { 78, 910, 1112 });
			first.Concat (second).AssertEquals (12, 34, 56, 78, 910, 1112);
		}

		[Test]
		public void Contains_IntsContainingPassedValue_ReturnsTrue ()
		{
			var source = Read (new [] { 12, -15, 21 });
			Assert.That (source.Contains (21), Is.True);
		}

		[Test]
		public void Contains_IntsThatDoNotContainPassedValue_ReturnsFalse ()
		{
			var source = Read (new [] { -2, 4, 8 });
			Assert.That (source.Contains (9), Is.False);
		}

		[Test]
		public void Contains_ListOfIntsContainingPassedValue_ReturnsTrue ()
		{
			var source = new List<int> { 1, 2, 3 };
			Assert.That (source.Contains (3), Is.True);
		}

		[Test]
		public void Count_Ints_ReturnsNumberOfElements ()
		{
			Assert.That (Read (new [] { 12, 34, 56 }).Count (), Is.EqualTo (3));
		}

		[Test]
		public void Count_PredicateArg_Strings_CountsOnlyStringsWithEvenLength ()
		{
			var source = new [] { "A", "AB", "ABC", "ABCD" };
			Assert.That (source.Count (s => s.Length % 2 == 0), Is.EqualTo (2));
		}

		[Test]
		public void DefaultIfEmpty_Inegers_YieldsIntegersInOrder ()
		{
			var source = Read (new [] { 12, 34, 56 });
			source.DefaultIfEmpty (1).AssertEquals (12, 34, 56);
		}

		[Test]
		public void DefaultIfEmpty_EmptyIntegersSource_ReturnsZero ()
		{
			var source = Read (new int [0]);
			source.DefaultIfEmpty ().AssertEquals (0);
		}

		[Test]
		public void DefaultIfEmpty_EmptyIntegersSourceWithNonZeroDefault_ReturnNonZeroDefault ()
		{
			var source = Read (new int [0]);
			source.DefaultIfEmpty (5).AssertEquals (5);
		}

		[Test]
		public void DefaultIfEmpty_DefaultValueArg_Integers_YieldsIntegersInOrder ()
		{
			var source = Read (new [] { 12, 34, 56 });
			source.DefaultIfEmpty (5).AssertEquals (12, 34, 56);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Distinct_NullSource_ThrowsArgumentNullException ()
		{
			Enumerable.Distinct<object> (null);
		}

		[Test]
		public void Distinct_IntegersWithSomeDuplicates_YieldsIntegersInSourceOrderWithoutDuplicates ()
		{
			var source = Read (new [] { 12, 34, 34, 56, 78, 78, 78, 910, 78 });
			source.Distinct ().AssertEquals (12, 34, 56, 78, 910);
		}

		[Test]
		public void Distinct_MixedSourceStringsWithCaseIgnoringComparer_YieldsFirstCaseOfEachDistinctStringInSourceOrder ()
		{
			var source = Read ("Foo Bar BAZ BaR baz FOo".Split ());
			source.Distinct (StringComparer.InvariantCultureIgnoreCase).AssertEquals ("Foo", "Bar", "BAZ");
		}

		[Test]
		[ExpectedException (typeof (ArgumentOutOfRangeException))]
		public void ElementAt_IndexOutOfRange_ThrowsArgumentOutOfRangeException ()
		{
			var source = Read (new [] { 3, 5, 7 });
			source.ElementAt (3);
		}

		[Test]
		public void ElementAt_Integers_ReturnsCorrectValues ()
		{
			var source = new [] { 15, 2, 7 };
			Assert.That (Read (source).ElementAt (0), Is.EqualTo (15));
			Assert.That (Read (source).ElementAt (1), Is.EqualTo (2));
			Assert.That (Read (source).ElementAt (2), Is.EqualTo (7));
		}

		[Test]
		[ExpectedException (typeof (ArgumentOutOfRangeException))]
		public void ElementAt_NegativeIndex_ThrowsArgumentOutOfRangeException ()
		{
			var source = new [] { 1, 2, 3 };
			source.ElementAt (-1);
		}

		[Test]
		public void ElementAtOrDefault_Integers_ReturnsZeroIfIndexOutOfRange ()
		{
			var source = Read (new [] { 3, 6, 8 });
			Assert.That (source.ElementAtOrDefault (3), Is.EqualTo (0));
		}

		[Test]
		public void ElementAtOrDefault_IntArray_ReturnsCorrectValue ()
		{
			var source = Read (new [] { 3, 6, 9 });
			Assert.That (source.ElementAtOrDefault (2), Is.EqualTo (9));
		}

		[Test]
		public void ElementAtOrDefault_ListOfInts_ReturnsCorrectElement ()
		{
			var source = new List<int> { 1, 2, 3, 4, 5, 6 };
			Assert.That (source.ElementAtOrDefault (2), Is.EqualTo (3));
		}

		[Test]
		public void ElementAtOrDefault_NegativeIndex_ReturnsDefault ()
		{
			var source = new [] { true, false, true, false };
			Assert.That (source.ElementAtOrDefault (-3), Is.False);
		}

		[Test]
		public void ElementAtOrDefault_ObjectArray_ReturnsNullIfIndexOutOfRange ()
		{
			var source = Read (new [] { new object (), new object () });
			Assert.That (source.ElementAtOrDefault (2), Is.EqualTo (null));
		}

		[Test]
		public void ElementAtOrDefault_ObjectArray_ReturnsCorrectValue ()
		{
			var first = new object ();
			var source = Read (new [] { first, new object () });
			Assert.That (source.ElementAt (0), Is.EqualTo (first));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Except_secondArg_ArgumentNull_ThrowsArgumentNullException ()
		{
			Read<object> ().Except (null);
		}

		[Test]
		public void Except_SecondArg_ValidArgument_ReturnsCorrectEnumerable () // TODO Improve test name
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
			var argument = Read (new [] { 1, 3, 5, 7, 9 });
			source.Except (argument).AssertEquals (2, 4, 6, 8, 10);
		}

		[Test]
		public void Except_SecondArgComparerArg_ComparerIsUsed ()
		{
			var source = Read (new [] { "albert", "john", "simon" });
			var argument = Read (new [] { "ALBERT" });
			source.Except (argument, StringComparer.CurrentCultureIgnoreCase).AssertEquals ("john", "simon");
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void First_EmptySource_ThrowsInvalidOperationException ()
		{
			Read<int> ().First ();
		}

		[Test]
		public void First_Integers_ReturnsFirst ()
		{
			var source = Read (new [] { 12, 34, 56 });
			Assert.That (source.First (), Is.EqualTo (12));
		}

		[Test]
		public void First_IntegersWithEvensPredicate_FirstEvenInteger ()
		{
			var source = Read (new [] { 15, 20, 25, 30 });
			Assert.That (source.First (i => i % 2 == 0), Is.EqualTo (20));
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void First_IntegersWithNonMatchingPredicate_ThrowsInvalidOperationException ()
		{
			var source = Read (new [] { 12, 34, 56, 78 });
			Assert.That (source.First (i => i > 100), Is.EqualTo (0));
		}

		[Test]
		public void FirstOrDefault_EmptyBooleanSource_ReturnsFalse ()
		{
			Assert.That (Read<bool> ().FirstOrDefault (), Is.False);
		}

		[Test]
		public void FirstOrDefault_Objects_ReturnsFirstReference ()
		{
			var first = new object ();
			var source = Read (new [] { first, new object () });
			Assert.That (source.FirstOrDefault (), Is.SameAs (first));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void FirstOrDefault_PredicateArg_NullAsPredicate_ThrowsArgumentNullException ()
		{
			var source = new [] { 3, 5, 7 };
			source.FirstOrDefault (null);
		}

		[Test]
		public void FirstOrDefault_PredicateArg_ValidPredicate_ReturnsFirstMatchingItem ()
		{
			var source = Read (new [] { 1, 4, 8 });
			Assert.That (source.FirstOrDefault (i => i % 2 == 0), Is.EqualTo (4));
		}

		[Test]
		public void FirstOrDefault_PredicateArg_NoMatchesInArray_ReturnsDefaultValueOfType ()
		{
			var source = Read (new [] { 1, 4, 6 });
			Assert.That (source.FirstOrDefault (i => i > 10), Is.EqualTo (0));
		}

		private class Person {
			public string FirstName { get; set; }
			public string FamilyName { get; set; }
			public int Age { get; set; }
			public static Person [] CreatePersons ()
			{
				return new []
                           {
                               new Person {FamilyName = "M\u00FCller", FirstName = "Peter", Age = 21},
                               new Person {FamilyName = "M\u00FCller", FirstName = "Herbert", Age = 22},
                               new Person {FamilyName = "Meier", FirstName = "Hubert", Age = 23},
                               new Person {FamilyName = "Meier", FirstName = "Isidor", Age = 24}
                           };
			}
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void GroupBy_KeySelectorArg_NullAsKeySelector_ThrowsArgumentNullException ()
		{
			Read<object> ().GroupBy<object, object> (null);
		}

		[Test]
		public void GroupBy_KeySelectorArg_ValidArguments_CorrectGrouping ()
		{
			var persons = Read (Person.CreatePersons ());
			var result = new Reader<IGrouping<string, Person>> (persons.GroupBy (person => person.FamilyName));

			var mueller = result.Read ();
			Assert.That (mueller.Key, Is.EqualTo ("M\u00FCller"));
			Assert.That (Array.ConvertAll (ToArray (mueller), p => p.FirstName),
						Is.EqualTo (new [] { "Peter", "Herbert" }));

			var meier = result.Read ();
			Assert.That (meier.Key, Is.EqualTo ("Meier"));
			Assert.That (Array.ConvertAll (ToArray (meier), p => p.FirstName),
						Is.EqualTo (new [] { "Hubert", "Isidor" }));

			result.AssertEnded ();
		}

		private static T [] ToArray<T> (IEnumerable<T> source)
		{
			return new List<T> (source).ToArray ();
		}

		[Test]
		// TODO: make better
		public void GroupBy_KeySelectorArg_ValidArguments_CorrectCaseSensitiveGrouping ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter"},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert"},
                new Person {FamilyName = "Meier", FirstName = "Hubert"},
                new Person {FamilyName = "meier", FirstName = "Isidor"}
            });
			var result = persons.GroupBy (person => person.FamilyName);
			var enumerator = result.GetEnumerator ();
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("M\u00FCller"));
			Assert.That (enumerator.Current.ElementAt (0).FirstName, Is.EqualTo ("Peter"));
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("m\u00FCller"));
			Assert.That (enumerator.Current.ElementAt (0).FirstName, Is.EqualTo ("Herbert"));
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("Meier"));
			Assert.That (enumerator.Current.ElementAt (0).FirstName, Is.EqualTo ("Hubert"));
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("meier"));
			Assert.That (enumerator.Current.ElementAt (0).FirstName, Is.EqualTo ("Isidor"));

			Assert.That (enumerator.MoveNext (), Is.False);
		}

		[Test]
		public void GroupBy_KeySelectorArgComparerArg_KeysThatDifferInCasingNonCaseSensitiveStringComparer_CorrectGrouping ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter"},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert"},
                new Person {FamilyName = "Meier", FirstName = "Hubert"},
                new Person {FamilyName = "meier", FirstName = "Isidor"}
            });
			var result = persons.GroupBy (person => person.FamilyName, StringComparer.InvariantCultureIgnoreCase);
			var enumerator = result.GetEnumerator ();
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("M\u00FCller"));
			Assert.That (enumerator.Current.ElementAt (0).FirstName, Is.EqualTo ("Peter"));
			Assert.That (enumerator.Current.ElementAt (1).FirstName, Is.EqualTo ("Herbert"));

			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("Meier"));
			Assert.That (enumerator.Current.ElementAt (0).FirstName, Is.EqualTo ("Hubert"));
			Assert.That (enumerator.Current.ElementAt (1).FirstName, Is.EqualTo ("Isidor"));

			Assert.That (enumerator.MoveNext (), Is.False);
		}

		[Test]
		public void GroupBy_KeySelectorArgElementSelectorArg_ValidArguments_CorrectGroupingAndProjection ()
		{
			var enumerable = Read (Person.CreatePersons ());
			var result = enumerable.GroupBy (person => person.FamilyName, person => person.Age);
			var enumerator = result.GetEnumerator ();
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("M\u00FCller"));
			Assert.That (enumerator.Current.ElementAt (0), Is.EqualTo (21));
			Assert.That (enumerator.Current.ElementAt (1), Is.EqualTo (22));

			enumerator.MoveNext ();
			Assert.That (enumerator.Current.Key, Is.EqualTo ("Meier"));
			Assert.That (enumerator.Current.ElementAt (0), Is.EqualTo (23));
			Assert.That (enumerator.Current.ElementAt (1), Is.EqualTo (24));
		}

		[Test]
		public void GroupBy_KeySelectorArgResultSelectorArg_ValidArguments_CorrectGroupingProcessing ()
		{
			var persons = Read (Person.CreatePersons ());

			IEnumerable<int> result = persons.GroupBy (person => person.FamilyName,
												(key, group) => {
													int ageSum = 0;
													foreach (Person p in group) {
														ageSum += p.Age;
													}
													return ageSum;
												}
												);
			result.AssertEquals (43, 47);
		}

		[Test]
		public void GroupByKey_KeySelectorArgElementSelectorArgComparerArg_ValidArguments_CorrectGroupingAndProcessing ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter", Age = 21},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert", Age = 22},
                new Person {FamilyName = "Meier", FirstName = "Hubert", Age= 23},
                new Person {FamilyName = "meier", FirstName = "Isidor", Age = 24}
            });

			IEnumerable<IGrouping<string, int>> result = persons.GroupBy (person => person.FamilyName,
												person => person.Age,
												StringComparer.CurrentCultureIgnoreCase);
			IEnumerator<IGrouping<string, int>> enumerator = result.GetEnumerator ();
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.ElementAt (0), Is.EqualTo (21));
			Assert.That (enumerator.Current.ElementAt (1), Is.EqualTo (22));
			enumerator.MoveNext ();
			Assert.That (enumerator.Current.ElementAt (0), Is.EqualTo (23));
			Assert.That (enumerator.Current.ElementAt (1), Is.EqualTo (24));
			Assert.That (enumerator.MoveNext (), Is.False);
		}

		[Test]
		public void GroupBy_KeySelectorArgElementSelectorArgResultSelectorArg_ValidArguments_CorrectGroupingAndTransforming ()
		{
			var persons = Read (Person.CreatePersons ());
			var result = persons.GroupBy (p => p.FamilyName, p => p.Age,
																	  (name, enumerable2) => {
																		  int totalAge = 0;
																		  foreach (var i in enumerable2) {
																			  totalAge += i;
																		  }
																		  return totalAge;
																	  });
			result.AssertEquals (43, 47);
		}

		[Test]
		public void GroupBy_KeySelectorArgResultSelectorArgComparerArg_ValidArguments_CorrectGroupingAndTransforming ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter", Age = 21},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert", Age = 22},
                new Person {FamilyName = "Meier", FirstName = "Hubert", Age= 23},
                new Person {FamilyName = "meier", FirstName = "Isidor", Age = 24}
            });
			var result = persons.GroupBy (p => p.FamilyName,
																	  (name, enumerable2) => {
																		  int totalAge = 0;
																		  foreach (var i in enumerable2) {
																			  totalAge += i.Age;
																		  }
																		  return totalAge;
																	  },
																	  StringComparer.CurrentCultureIgnoreCase);
			result.AssertEquals (43, 47);
		}

		[Test]
		public void GroupBy_KeySelectorArgElementSelectorArgResultSelectorArgComparerArg_ValidArguments_CorrectGroupingAndTransforming ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter", Age = 21},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert", Age = 22},
                new Person {FamilyName = "Meier", FirstName = "Hubert", Age= 23},
                new Person {FamilyName = "meier", FirstName = "Isidor", Age = 24}
            });
			var result = persons.GroupBy (p => p.FamilyName, p => p.Age,
																	  (name, enumerable2) => {
																		  int totalAge = 0;
																		  foreach (var i in enumerable2) {
																			  totalAge += i;
																		  }
																		  return totalAge;
																	  }, StringComparer.CurrentCultureIgnoreCase);
			result.AssertEquals (43, 47);
		}

		class Pet {
			public string Name { get; set; }
			public string Owner { get; set; }
		}

		[Test]
		public void GroupJoin_InnerArgOuterKeySelectorArgInnerKeySelectorArgResultSelectorArg_ValidArguments_CorrectGroupingAndJoining ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter", Age = 21},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert", Age = 22},
                new Person {FamilyName = "Meier", FirstName = "Hubert", Age= 23},
                new Person {FamilyName = "meier", FirstName = "Isidor", Age = 24}
            });

			var pets = Read (new []
            {
                new Pet {Name = "Barley", Owner = "Peter"},
                new Pet {Name = "Boots", Owner = "Herbert"},
                new Pet {Name = "Whiskers", Owner = "Herbert"},
                new Pet {Name = "Daisy", Owner = "Isidor"}
            });

			var result = persons.GroupJoin (pets, person => person.FirstName, pet => pet.Owner,
							  (person, petCollection) =>
							  new { OwnerName = person.FirstName, Pets = petCollection.Select (pet => pet.Name) });

			var enumerator = result.GetEnumerator ();
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Peter"));
			var petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Barley"));
			Assert.That (petEnumerator.MoveNext (), Is.False);
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Herbert"));
			petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Boots"));
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Whiskers"));
			Assert.That (petEnumerator.MoveNext (), Is.False);
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Hubert"));
			petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			Assert.That (petEnumerator.MoveNext (), Is.False);
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Isidor"));
			petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Daisy"));
			Assert.That (petEnumerator.MoveNext (), Is.False);
			Assert.That (enumerator.MoveNext (), Is.False);

			//foreach (var owner in result) {
			//    Debug.WriteLine(owner.OwnerName);
			//    Debug.Indent();
			//    foreach (var petName in owner.Pets) {
			//        Debug.WriteLine("    " + petName);
			//    }
			//    Debug.Unindent();
			//}
		}

		[Test]
		public void GroupJoin_InnerArgOuterKeySelectorArgInnerKeySelectorArgResultSelectorArgComparerArg_ValidArguments_CorrectGroupingAndJoining ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter", Age = 21},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert", Age = 22},
                new Person {FamilyName = "Meier", FirstName = "Hubert", Age= 23},
                new Person {FamilyName = "meier", FirstName = "Isidor", Age = 24}
            });

			var pets = Read (new []
            {
                new Pet {Name = "Barley", Owner = "Peter"},
                new Pet {Name = "Boots", Owner = "Herbert"},
                new Pet {Name = "Whiskers", Owner = "herbert"}, // This pet is not associated to "Herbert"
                new Pet {Name = "Daisy", Owner = "Isidor"}
            });

			var result = persons.GroupJoin (pets, person => person.FirstName, pet => pet.Owner,
							  (person, petCollection) =>
							  new { OwnerName = person.FirstName, Pets = petCollection.Select (pet => pet.Name) },
							  StringComparer.CurrentCultureIgnoreCase);

			var enumerator = result.GetEnumerator ();
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Peter"));
			var petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Barley"));
			Assert.That (petEnumerator.MoveNext (), Is.False);
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Herbert"));
			petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Boots"));
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Whiskers"));
			Assert.That (petEnumerator.MoveNext (), Is.False);
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Hubert"));
			petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			Assert.That (petEnumerator.MoveNext (), Is.False);
			enumerator.MoveNext (); Assert.That (enumerator.Current.OwnerName, Is.EqualTo ("Isidor"));
			petEnumerator = enumerator.Current.Pets.GetEnumerator ();
			petEnumerator.MoveNext (); Assert.That (petEnumerator.Current, Is.EqualTo ("Daisy"));
			Assert.That (petEnumerator.MoveNext (), Is.False);
			Assert.That (enumerator.MoveNext (), Is.False);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void GroupJoin_InnerArgOuterKeySelectorArgInnerKeySelectorArgResultSelectorArg_PassNullAsOuterKeySelector_ThrowsArgumentNullException ()
		{
			var persons = Read (new []
            {
                new Person {FamilyName = "M\u00FCller", FirstName = "Peter", Age = 21},
                new Person {FamilyName = "m\u00FCller", FirstName = "Herbert", Age = 22},
                new Person {FamilyName = "Meier", FirstName = "Hubert", Age= 23},
                new Person {FamilyName = "meier", FirstName = "Isidor", Age = 24}
            });

			var pets = Read (new []
            {
                new Pet {Name = "Barley", Owner = "Peter"},
                new Pet {Name = "Boots", Owner = "Herbert"},
                new Pet {Name = "Whiskers", Owner = "Herbert"},
                new Pet {Name = "Daisy", Owner = "Isidor"}
            });

			persons.GroupJoin (pets, null, pet => pet.Owner,
							  (person, petCollection) =>
							  new { OwnerName = person.FirstName, Pets = petCollection.Select (pet => pet.Name) });
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Intersect_NullSecondSource_ThrowsArgumentNullException ()
		{
			Read<object> ().Intersect (null);
		}

		[Test]
		public void Intersect_IntegerSources_YieldsCommonSet ()
		{
			var first = Read (new [] { 1, 2, 3 });
			var second = Read (new [] { 2, 3, 4 });
			first.Intersect (second).AssertEquals (2, 3);
		}

		[Test]
		public void Intersect_StringSourcesWithMixedCasingAndCaseInsensitiveComparer_YieldsCommonSetFromFirstSource ()
		{
			var first = Read (new [] { "Heinrich", "Hubert", "Thomas" });
			var second = Read (new [] { "Heinrich", "hubert", "Joseph" });
			var result = first.Intersect (second, StringComparer.CurrentCultureIgnoreCase);
			result.AssertEquals ("Heinrich", "Hubert");
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Join_InnerArgOuterKeySelectorArgInnerKeySelectorArgResultSelectorArg_PassNullAsArgument_ThrowsArgumentNullException ()
		{
			Read<object> ().Join<object, object, object, object> (null, null, null, null);
		}

		[Test]
		public void Join_InnerArgOuterKeySelectorArgInnerKeySelectorArgResultSelectorArg_PassingPetsAndOwners_PetsAreCorrectlyAssignedToOwners ()
		{
			var persons = Read (Person.CreatePersons ());
			var pets = new Reader<Pet> (new []
                           {
                               new Pet {Name = "Barley", Owner = "Peter"},
                               new Pet {Name = "Boots", Owner = "Herbert"},
                               new Pet {Name = "Whiskers", Owner = "Herbert"},
                               new Pet {Name = "Daisy", Owner = "Isidor"}
                           });
			var result = persons.Join (pets, aPerson => aPerson.FirstName, aPet => aPet.Owner,
						 (aPerson, aPet) => new { Owner = aPerson.FirstName, Pet = aPet.Name });

			var enumerator = result.GetEnumerator ();
			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Peter"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Barley"));

			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Herbert"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Boots"));

			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Herbert"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Whiskers"));

			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Isidor"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Daisy"));

			Assert.That (enumerator.MoveNext (), Is.False);
		}

		[Test]
		public void Join_InnerArgOuterKeySelectorArgInnerKeySelectorArgResultSelectorArgComparerArg_PetOwnersNamesCasingIsInconsistent_CaseInsensitiveJoinIsPerformed ()
		{
			var persons = Read (Person.CreatePersons ());
			var pets = new Reader<Pet> (new []
                           {
                               new Pet {Name = "Barley", Owner = "Peter"},
                               new Pet {Name = "Boots", Owner = "Herbert"},
                               new Pet {Name = "Whiskers", Owner = "herbert"},
                               new Pet {Name = "Daisy", Owner = "Isidor"}
                           });
			var result = persons.Join (pets, aPerson => aPerson.FirstName, aPet => aPet.Owner,
						 (aPerson, aPet) => new { Owner = aPerson.FirstName, Pet = aPet.Name },
						 StringComparer.CurrentCultureIgnoreCase);

			var enumerator = result.GetEnumerator ();
			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Peter"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Barley"));

			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Herbert"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Boots"));

			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Herbert"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Whiskers"));

			Assert.That (enumerator.MoveNext (), Is.True);
			Assert.That (enumerator.Current.Owner, Is.EqualTo ("Isidor"));
			Assert.That (enumerator.Current.Pet, Is.EqualTo ("Daisy"));

			Assert.That (enumerator.MoveNext (), Is.False);

			//foreach (var i in result) {
			//    Debug.WriteLine(String.Format("Owner = {0}; Pet = {1}", i.Owner, i.Pet));
			//}
		}

		[Test]
		public void Last_Integers_ReturnsLastElement ()
		{
			var source = Read (new [] { 1, 2, 3 });
			Assert.That (source.Last (), Is.EqualTo (3));
		}

		[Test]
		public void Last_IntegerListOptimization_ReturnsLastElementWithoutEnumerating ()
		{
			var source = new NonEnumerableList<int> (new [] { 1, 2, 3 });
			Assert.That (source.Last (), Is.EqualTo (3));
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Last_EmptyIntegerListOptimization_ThrowsInvalidOperationException ()
		{
			new NonEnumerableList<int> ().Last ();
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Last_PredicateArg_NullAsPredicate_ThrowsArgumentNullException ()
		{
			Read<object> ().Last (null);
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Last_PredicateArg_NoMatchingElement_ThrowsInvalidOperationException ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			source.Last (i => i > 10);
		}

		[Test]
		public void Last_PredicateArg_ListOfInts_ReturnsLastMatchingElement ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			Assert.That (source.Last (i => i % 2 == 0), Is.EqualTo (4));
		}

		[Test]
		public void LastOrDefault_EmptySource_ReturnsZero ()
		{
			var source = Read (new int [0]);
			Assert.That (source.LastOrDefault (), Is.EqualTo (0));
		}

		[Test]
		public void LastOrDefault_NonEmptyList_ReturnsLastElement ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			Assert.That (source.LastOrDefault (), Is.EqualTo (5));
		}

		[Test]
		public void LastOrDefault_PredicateArg_ValidArguments_RetunsLastMatchingElement ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			Assert.That (source.LastOrDefault (i => i % 2 == 0), Is.EqualTo (4));
		}

		[Test]
		public void LastOrDefault_PredicateArg_NoMatchingElement_ReturnsZero ()
		{
			var source = Read (new [] { 1, 3, 5, 7 });
			Assert.That (source.LastOrDefault (i => i % 2 == 0), Is.EqualTo (0));
		}

		[Test]
		public void LongCount_ValidArgument_ReturnsCorrectNumberOfElements ()
		{
			var source = Read (new [] { 1, 4, 7, 10 });
			Assert.That (source.LongCount (), Is.EqualTo (4));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void LongCount_PredicateArg_NullAsPredicate_ThrowsArgumentNullException ()
		{
			Read<object> ().LongCount (null);
		}

		[Test]
		public void LongCount_PredicateArg_ValidArguments_ReturnsCorrectNumerOfMatchingElements ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			Assert.That (source.LongCount (i => i % 2 == 0), Is.EqualTo (2));
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Max_EmptyList_ThrowsInvalidOperationException ()
		{
			var source = Read (new int [0]);
			source.Max ();
		}

		[Test]
		public void Max_EmptyNullableIntegerArray_ReturnsNull ()
		{
			Assert.That (Read (new int? [0]).Max (), Is.Null);
		}

		[Test]
		public void Max_NullableIntegerArrayWithNullsOnly_ReturnsNull ()
		{
			Assert.That (Read (new int? [] { null, null, null }).Max (), Is.Null);
		}

		[Test]
		public void Max_Integers_ReturnsMaxValue ()
		{
			var source = Read (new [] { 1000, 203, -9999 });
			Assert.That (source.Max (), Is.EqualTo (1000));
		}

		[Test]
		public void Max_NullableLongs_ReturnsMaxValue ()
		{
			Assert.That (Read (new long? [] { 1L, 2L, 3L, null }).Max (), Is.EqualTo (3));
		}

		[Test]
		public void Max_NullableDoubles_ReturnsMaxValue ()
		{
			Assert.That (Read (new double? [] { 1, 2, 3, null }).Max (), Is.EqualTo (3));
		}

		[Test]
		public void Max_NullableDecimals_ReturnsMaxValue ()
		{
			Assert.That (Read (new decimal? [] { 1m, 2m, 3m, null }).Max (), Is.EqualTo (3));
		}

		[Test]
		public void Max_NullableFloats_ReturnsMaxValue ()
		{
			Assert.That (Read (new float? [] { -1000, -100, -1, null }).Max (), Is.EqualTo (-1));
		}

		[Test]
		public void Max_ListWithNullableType_ReturnsMaximum ()
		{
			var source = Read (new int? [] { 1, 4, null, 10 });
			Assert.That (source.Max (), Is.EqualTo (10));
		}

		[Test]
		public void Max_NullableList_ReturnsMaxNonNullValue ()
		{
			var source = Read (new int? [] { -5, -2, null });
			Assert.That (source.Max (), Is.EqualTo (-2));
		}

		[Test]
		public void Max_SelectorArg_ListOfObjects_ReturnsMaxSelectedValue ()
		{
			var persons = Read (Person.CreatePersons ());
			Assert.That (persons.Max (p => p.Age), Is.EqualTo (24));
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Min_EmptyList_ThrowsInvalidOperationException ()
		{
			var source = Read<int> ();
			source.Min ();
		}

		[Test]
		public void Min_IntegersWithSomeNull_ReturnsMinimumNonNullValue ()
		{
			var source = Read (new int? [] { 199, 15, null, 30 });
			Assert.That (source.Min (), Is.EqualTo (15));
		}

		[Test]
		public void Min_NullableLongs_ReturnsMinimumNonNullValue ()
		{
			var source = Read (new long? [] { 199, 15, null, 30 });
			Assert.That (source.Min (), Is.EqualTo (15));
		}

		[Test]
		public void Min_NullableFloats_ReturnsMinimumNonNullValue ()
		{
			var source = Read (new float? [] { 1.111f, null, 2.222f });
			Assert.That (source.Min (), Is.EqualTo (1.111f).Within (0.01));
		}

		[Test]
		public void Min_NullableDoubles_ReturnsMinimumNonNullValue ()
		{
			var source = Read (new double? [] { 1.111, null, 2.222 });
			Assert.That (source.Min (), Is.EqualTo (1.111).Within (0.01));
		}

		[Test]
		public void Min_NullableDecimals_ReturnsMinimumNonNullValue ()
		{
			var source = Read (new decimal? [] { 1.111m, null, 2.222m });
			Assert.That (source.Min (), Is.EqualTo (1.111m).Within (0.01));
		}

		[Test]
		public void Min_StringsWithLengthSelector_ReturnsMinimumNonNullStringLength ()
		{
			var strings = Read (new [] { "five", "four", null, "three", null, "two", "one", "zero" });
			Assert.That (strings.Min (s => s != null ? s.Length : (int?) null), Is.EqualTo (3));
		}

		[Test]
		public void OfType_EnumerableWithElementsOfDifferentTypes_OnlyDecimalsAreReturned ()
		{
			// ...................V----V Needed for Mono (CS0029)
			var source = Read (new object [] { 1, "Hello", 1.234m, new object () });
			var result = source.OfType<decimal> ();
			result.AssertEquals (1.234m);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void OrderBy_KeySelectorArg_NullAsKeySelector_ThrowsArgumentNullException ()
		{
			Read<object> ().OrderBy<object, object> (null);
		}

		[Test]
		public void OrderBy_KeySelector_ArrayOfPersons_PersonsAreOrderedByAge ()
		{
			var persons = Person.CreatePersons ();
			var reversePersons = (Person []) persons.Clone ();
			Array.Reverse (reversePersons);
			var source = Read (reversePersons);
			var result = source.OrderBy (p => p.Age);

			var age = 21;
			foreach (var person in result)
				Assert.That (person.Age, Is.EqualTo (age++));

			Assert.That (age, Is.EqualTo (25));
		}

		[Test]
		public void OrderBy_KeySelector_DataWithDuplicateKeys_YieldsStablySortedData ()
		{
			var data = new []
            {
                new { Number = 4, Text = "four" },
                new { Number = 4, Text = "quatre" },
                new { Number = 4, Text = "vier" },
                new { Number = 4, Text = "quattro" },
                new { Number = 1, Text = "one" },
                new { Number = 2, Text = "two" },
                new { Number = 2, Text = "deux" },
                new { Number = 3, Text = "three" },
                new { Number = 3, Text = "trois" },
                new { Number = 3, Text = "drei" },
            };

			var result = Read (data).OrderBy (e => e.Number);
			using (var e = result.GetEnumerator ()) {
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("one"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("two"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("deux"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("three"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("trois"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("drei"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("four"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("quatre"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("vier"));
				e.MoveNext (); Assert.That (e.Current.Text, Is.EqualTo ("quattro"));
				Assert.That (e.MoveNext (), Is.False);
			}
		}

		[Test]
		public void ThenBy_KeySelector_DataWithDuplicateKeys_YieldsStablySortedData ()
		{
			var data = new []
            {
                new { Position = 1, LastName = "Smith", FirstName = "John" },
                new { Position = 2, LastName = "Smith", FirstName = "Jack" },
                new { Position = 3, LastName = "Smith", FirstName = "John" },
                new { Position = 4, LastName = "Smith", FirstName = "Jack" },
                new { Position = 5, LastName = "Smith", FirstName = "John" },
                new { Position = 6, LastName = "Smith", FirstName = "Jack" },
            };

			var result = Read (data).OrderBy (e => e.LastName).ThenBy (e => e.FirstName);
			using (var e = result.GetEnumerator ()) {
				e.MoveNext (); Assert.That (e.Current.Position, Is.EqualTo (2));
				e.MoveNext (); Assert.That (e.Current.Position, Is.EqualTo (4));
				e.MoveNext (); Assert.That (e.Current.Position, Is.EqualTo (6));
				e.MoveNext (); Assert.That (e.Current.Position, Is.EqualTo (1));
				e.MoveNext (); Assert.That (e.Current.Position, Is.EqualTo (3));
				e.MoveNext (); Assert.That (e.Current.Position, Is.EqualTo (5));
				Assert.That (e.MoveNext (), Is.False);
			}
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void ThenBy_NullSource_ThrowsArgumentNullException ()
		{
			Enumerable.ThenBy<object, object> (null, e => { throw new NotImplementedException (); });
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void ThenBy_NullKeySelector_ThrowsArgumentNullException ()
		{
			Read<object> ().OrderBy<object, object> (e => { throw new NotImplementedException (); }).ThenBy<object, object> (null);
		}
		/// <summary>
		/// To sort ints in descending order.
		/// </summary>
		class ReverseComparer : IComparer<int> {
			public int Compare (int x, int y)
			{
				return y.CompareTo (x);
			}
		}

		[Test]
		public void ThenByDescending_KeySelectorArgComparerArg_StringArray_CorrectOrdering ()
		{
			var source = Read (new [] { "AA", "AB", "AC", "-BA", "-BB", "-BC" });
			var result = source.OrderBy (s => s.ToCharArray () [s.ToCharArray ().Length - 1]).ThenByDescending (s => s.Length); /*.AssertEquals("butterfly", "elephant", "dog", "snake", "ape"); */
			result.AssertEquals ("-BA", "AA", "-BB", "AB", "-BC", "AC");
		}

		[Test]
		public void OrderBy_KeySelectorArgComparerArg_ArrayOfPersonsAndReversecomparer_PersonsAreOrderedByAgeUsingReversecomparer ()
		{
			var persons = Read (Person.CreatePersons ());
			var result = persons.OrderBy (p => p.Age, new ReverseComparer ());
			var age = 25;
			foreach (var person in result) {
				age--;
				Assert.That (person.Age, Is.EqualTo (age));
			}
			Assert.That (age, Is.EqualTo (21));

		}

		[Test]
		public void OrderByDescending_KeySelectorArg_ArrayOfPersons_PersonsAreOrderedByAgeDescending ()
		{
			var persons = Read (Person.CreatePersons ());
			var result = persons.OrderByDescending (p => p.Age);
			int age = 25;
			foreach (var person in result) {
				age--;
				Assert.That (person.Age, Is.EqualTo (age));
			}
			Assert.That (age, Is.EqualTo (21));
		}

		[Test]
		[ExpectedException (typeof (ArgumentOutOfRangeException))]
		public void Range_ProduceRangeThatLeadsToOverflow_ThrowsArgumentOutOfRangeException ()
		{
			Enumerable.Range (int.MaxValue - 3, 5);
		}

		[Test]
		[ExpectedException (typeof (ArgumentOutOfRangeException))]
		public void Range_NegativeCount_ThrowsArgumentOutOfRangeException ()
		{
			Enumerable.Range (0, -1);
		}

		[Test]
		public void Range_Start10Count5_IntsFrom10To14 ()
		{
			var result = Enumerable.Range (10, 5);
			result.AssertEquals (10, 11, 12, 13, 14);
		}

		[Test]
		[ExpectedException (typeof (ArgumentOutOfRangeException))]
		public void Repeat_PassNegativeCount_ThrowsArgumentOutOfRangeException ()
		{
			Enumerable.Repeat ("Hello World", -2);
		}

		[Test]
		public void Repeat_StringArgumentCount2_ReturnValueContainsStringArgumentTwice ()
		{
			var result = Enumerable.Repeat ("Hello World", 2);
			result.AssertEquals ("Hello World", "Hello World");
		}

		[Test]
		public void Reverse_SeriesOfInts_IntsAreCorrectlyReversed ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			source.Reverse ().AssertEquals (5, 4, 3, 2, 1);
		}

		[Test]
		public void Select_ArrayOfPersons_AgeOfPersonsIsSelectedAccordingToPassedLambdaExpression ()
		{
			var persons = Read (Person.CreatePersons ());
			persons.Select (p => p.Age).AssertEquals (21, 22, 23, 24);
		}

		[Test]
		public void Select_SelectorArg_LambdaThatTakesIndexAsArgument_ReturnValueContainsElementsMultipliedByIndex ()
		{
			var source = Read (new [] { 0, 1, 2, 3 });
			source.Select ((i, index) => i * index).AssertEquals (0, 1, 4, 9);
		}

		[Test]
		public void SelectMany_SelectorArg_ArrayOfPersons_ReturnsASequenceWithAllLettersOfFirstnames ()
		{
			var persons = Read (Person.CreatePersons ());
			var result = persons.SelectMany (p => p.FirstName.ToCharArray ());
			var check = "PeterHerbertHubertIsidor".ToCharArray ();
			int count = 0;
			foreach (var c in result) {
				Assert.That (c, Is.EqualTo (check [count]));
				count++;
			}
		}

		class PetOwner {
			public string Name { get; set; }
			public List<string> Pets { get; set; }
		}

		[Test]
		public void SelectMany_Selector3Arg_ArrayOfPetOwners_SelectorUsesElementIndexArgument ()
		{
			var petOwners = Read (new []
                { new PetOwner { Name="Higa, Sidney",
                      Pets = new List<string>{ "Scruffy", "Sam" } },
                  new PetOwner { Name="Ashkenazi, Ronen",
                      Pets = new List<string>{ "Walker", "Sugar" } },
                  new PetOwner { Name="Price, Vernette",
                      Pets = new List<string>{ "Scratches", "Diesel" } },
                  new PetOwner { Name="Hines, Patrick",
                      Pets = new List<string>{ "Dusty" } } });
			IEnumerable<string> result =
				petOwners.SelectMany ((petOwner, index) =>
							 petOwner.Pets.Select (pet => index + pet));
			result.AssertEquals ("0Scruffy", "0Sam", "1Walker", "1Sugar", "2Scratches", "2Diesel", "3Dusty");
		}

		[Test]
		[Category ("NotWorking")]
		public void SelectMany_CollectionSelectorArgResultSelectorArg_ArrayOfPetOwner_ResultContainsElementForEachPetAPetOwnerHas ()
		{
			var petOwners = Read (new []
                { new PetOwner { Name="Higa",
                      Pets = new List<string>{ "Scruffy", "Sam" } },
                  new PetOwner { Name="Ashkenazi",
                      Pets = new List<string>{ "Walker", "Sugar" } },
                  new PetOwner { Name="Price",
                      Pets = new List<string>{ "Scratches", "Diesel" } },
                  new PetOwner { Name="Hines",
                      Pets = new List<string>{ "Dusty" } } });
			var result = petOwners.SelectMany (petOwner => petOwner.Pets, (petOwner, petName) => new { petOwner.Name, petName });

			// compare result with result from Microsoft implementation
			var sb = new StringBuilder ();
			foreach (var s in result) {
				sb.Append (s.ToString ());
			}
			Assert.That (sb.ToString (), Is.EqualTo ("{ Name = Higa, petName = Scruffy }{ Name = Higa, petName = Sam }{ Name = Ashkenazi, petName = Walker }{ Name = Ashkenazi, petName = Sugar }{ Name = Price, petName = Scratches }{ Name = Price, petName = Diesel }{ Name = Hines, petName = Dusty }"));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void SequenceEqual_NullFirstSequence_ThrowsArgumentNullException ()
		{
			Enumerable.SequenceEqual (null, Read<object> ());
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void SequenceEqual_NullSecondSequence_ThrowsArgumentNullException ()
		{
			Read<object> ().SequenceEqual (null);
		}

		[Test]
		public void SequenceEqual_EqualSequences_ReturnsTrue ()
		{
			var source = Read (new [] { 1, 2, 3 });
			var argument = Read (new [] { 1, 2, 3 });
			Assert.That (source.SequenceEqual (argument), Is.True);
		}

		[Test]
		public void SequenceEqual_DifferentSequences_ReturnsFalse ()
		{
			var source = Read (new [] { 1, 2, 3 });
			var argument = Read (new [] { 1, 3, 2 });
			Assert.That (source.SequenceEqual (argument), Is.False);
		}

		[Test]
		public void SequenceEqual_LongerSecondSequence_ReturnsFalse ()
		{
			var source = Read (new [] { 1, 2, 3 });
			var argument = Read (new [] { 1, 2, 3, 4 });
			Assert.That (source.SequenceEqual (argument), Is.False);
		}

		[Test]
		public void SequenceEqual_ShorterSecondSequence_ReturnsFalse ()
		{
			var first = Read (new [] { 1, 2, 3, 4 });
			var second = Read (new [] { 1, 2, 3 });
			Assert.That (first.SequenceEqual (second), Is.False);
		}

		[Test]
		public void SequenceEqual_FloatsWithTolerantComparer_ComparerIsUsed ()
		{
			var source = Read (new [] { 1f, 2f, 3f });
			var argument = Read (new [] { 1.03f, 1.99f, 3.02f });
			Assert.That (source.SequenceEqual (argument, new FloatComparer ()), Is.True);
		}

		private sealed class FloatComparer : IEqualityComparer<float> {
			public bool Equals (float x, float y)
			{
				return Math.Abs (x - y) < 0.1f;
			}
			public int GetHashCode (float x)
			{
				throw new NotImplementedException ();
			}
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Single_EmptySource_ThrowsInvalidOperationException ()
		{
			var source = Read<int> ();
			source.Single ();
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Single_SourceWithMoreThanOneElement_ThrowsInvalidOperationException ()
		{
			var source = Read (new [] { 3, 6 });
			source.Single ();
		}

		[Test]
		public void Single_SourceWithOneElement_ReturnsSingleElement ()
		{
			var source = Read (new [] { 1 });
			Assert.That (source.Single (), Is.EqualTo (1));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Single_PredicateArg_PassNullAsPredicate_ThrowsArgumentNullException ()
		{
			Read<object> ().Single (null);
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Single_PredicateArg_NoElementSatisfiesCondition_ThrowsInvalidOperationException ()
		{
			var source = Read (new [] { 1, 3, 5 });
			source.Single (i => i % 2 == 0);
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Single_PredicateArg_MoreThanOneElementSatisfiedCondition_ThrowsInvalidOperationException ()
		{
			var source = Read (new [] { 1, 2, 3, 4 });
			source.Single (i => i % 2 == 0);
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void Single_PredicateArg_SourceIsEmpty_ThrowsInvalidOperationException ()
		{
			var source = Read<int> ();
			source.Single (i => i % 2 == 0);
		}

		[Test]
		public void Single_PredicateArg_ArrayOfIntWithOnlyOneElementSatisfyingCondition_ReturnsOnlyThisElement ()
		{
			var source = Read (new [] { 1, 2, 3 });
			Assert.That (source.Single (i => i % 2 == 0), Is.EqualTo (2));
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void SingleOrDefault_MoreThanOneElementInSource_ThrowsInvalidOperationException ()
		{
			var source = Read (new [] { 1, 2, 3 });
			source.SingleOrDefault ();
		}

		[Test]
		public void SingleOrDefault_EmptySource_ReturnsZero ()
		{
			var source = Read<int> ();
			Assert.That (source.SingleOrDefault (), Is.EqualTo (0));
		}

		[Test]
		public void SingleOrDefault_SourceWithOneElement_ReturnsSingleElement ()
		{
			var source = Read (new [] { 5 });
			Assert.That (source.SingleOrDefault (), Is.EqualTo (5));
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void SingleOrDefault_PredicateArg_PassNullAsPredicate_ThrowsArgumentNullException ()
		{
			Read<object> ().SingleOrDefault (null);
		}

		[Test]
		public void SingleOrDefault_PredicateArg_EmptySource_ReturnsZero ()
		{
			var source = Read<int> ();
			Assert.That (source.SingleOrDefault (i => i % 2 == 0), Is.EqualTo (0));
		}

		[Test]
		[ExpectedException (typeof (InvalidOperationException))]
		public void SingleOrDefault_PredicateArg_MoreThanOneElementSatisfiesCondition_ThrowsInvalidOperationException ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			source.SingleOrDefault (i => i % 2 == 0);
		}

		[Test]
		public void SingleOrDefault_PredicateArg_NoElementSatisfiesCondition_ReturnsZero ()
		{
			var source = Read (new [] { 1, 3, 5 });
			Assert.That (source.SingleOrDefault (i => i % 2 == 0), Is.EqualTo (0));
		}

		[Test]
		public void SingleOrDefault_PredicateArg_OneElementSatisfiesCondition_ReturnsCorrectElement ()
		{
			var source = Read (new [] { 1, 2, 3 });
			Assert.That (source.SingleOrDefault (i => i % 2 == 0), Is.EqualTo (2));
		}

		[Test]
		public void Skip_IntsFromOneToTenAndFifeAsSecondArg_IntsFromSixToTen ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
			source.Skip (5).AssertEquals (6, 7, 8, 9, 10);
		}

		[Test]
		public void Skip_PassNegativeValueAsCount_SameBehaviorAsMicrosoftImplementation ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			source.Skip (-5).AssertEquals (1, 2, 3, 4, 5);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void SkipWhile_PredicateArg_PassNullAsPredicate_ThrowsArgumentNullException ()
		{
			Read<object> ().SkipWhile ((Func<object, bool>) null);
		}

		[Test]
		public void SkipWhile_PredicateArg_IntsFromOneToFive_ElementsAreSkippedAsLongAsConditionIsSatisfied ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			source.SkipWhile (i => i < 3).AssertEquals (3, 4, 5);
		}

		[Test]
		public void SkipWhile_PredicateArg_ArrayOfIntsWithElementsNotSatisfyingConditionAtTheEnd_IntsAtTheEndArePartOfResult ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 1, 2, 3 });
			source.SkipWhile (i => i < 3).AssertEquals (3, 4, 5, 1, 2, 3);
		}

		[Test]
		public void SkipWhile_PredicateArg_PredicateAlwaysTrue_EmptyResult ()
		{
			var source = Read (new [] { 1, 2, 3 });
			var result = source.SkipWhile (i => true);
			Assert.That (result.GetEnumerator ().MoveNext (), Is.False);
		}

		[Test]
		public void SkipWhile_Predicate3Arg_IntsFromOneToNine_ElementsAreSkippedWhileIndexLessThanFive ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9 });
			source.SkipWhile ((i, index) => index < 5).AssertEquals (6, 7, 8, 9);
		}

		[Test]
		[ExpectedException (typeof (OverflowException))]
		public void Sum_SumOfArgumentsCausesOverflow_ThrowsOverflowException ()
		{
			var source = Read (new [] { int.MaxValue - 1, 2 });
			source.Sum ();
		}

		[Test]
		public void Sum_IntsFromOneToTen_ResultIsFiftyFive ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
			Assert.That (source.Sum (), Is.EqualTo (55));
		}

		[Test]
		public void Sum_Longs_ReturnsSum ()
		{
			Assert.That (Read (new [] { 1L, 2L, 3L }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_Floats_ReturnsSum ()
		{
			Assert.That (Read (new [] { 1F, 2F, 3F }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_NullableFloats_ReturnsSum ()
		{
			Assert.That (Read (new float? [] { 1F, 2F, 3F, null }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_Doubles_ReturnsSum ()
		{
			Assert.That (Read (new double [] { 1, 2, 3 }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_NullableDoubles_ReturnsSum ()
		{
			Assert.That (Read (new double? [] { 1, 2, 3, null }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_Decimals_ReturnsSum ()
		{
			Assert.That (Read (new [] { 1m, 2m, 3m }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_NullableDecimals_ReturnsSum ()
		{
			Assert.That (Read (new decimal? [] { 1m, 2m, 3m, null }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_NullableLongs_ReturnsSum ()
		{
			Assert.That (Read (new long? [] { 1L, 2L, 3L, null }).Sum (), Is.EqualTo (6));
		}

		[Test]
		public void Sum_NullableIntsAsArguments_ReturnsCorrectSum ()
		{
			var source = Read (new int? [] { 1, 2, null });
			Assert.That (source.Sum (), Is.EqualTo (3));
		}

		[Test]
		public void Sum_SelectorArg_StringArray_ResultIsSumOfStringLengths ()
		{
			var source = Read (new [] { "dog", "cat", "eagle" });
			Assert.That (source.Sum (s => s.Length), Is.EqualTo (11));
		}

		[Test]
		public void Take_IntsFromOneToSixAndThreeAsCount_IntsFromOneToThreeAreReturned ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6 });
			source.Take (3).AssertEquals (1, 2, 3);
		}

		[Test]
		public void Take_CountBiggerThanList_ReturnsAllElements ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			source.Take (10).AssertEquals (1, 2, 3, 4, 5);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void TakeWhile_PassNullAsPredicate_ThrowsArgumentNullException ()
		{
			new object [0].TakeWhile ((Func<object, bool>) null);
		}

		[Test]
		public void TakeWhile_IntsFromOneToTenAndConditionThatSquareIsSmallerThan50_IntsFromOneToSeven ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
			source.TakeWhile (i => i * i < 50).AssertEquals (1, 2, 3, 4, 5, 6, 7);
		}

		[Test]
		public void ToArray_IntsFromOneToTen_ResultIsIntArrayContainingAllElements ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
			var result = source.ToArray ();
			Assert.That (result, Is.TypeOf (typeof (int [])));
			result.AssertEquals (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void ToDictionary_KeySelectorArg_KeySelectorYieldsNull_ThrowsArgumentNullException ()
		{
			var source = new [] { "eagle", "deer" };
			source.ToDictionary<string, string> (s => null);
		}

		[Test]
		[ExpectedException (typeof (ArgumentException))]
		public void ToDictionary_KeySelectorArg_DuplicateKeys_ThrowsArgumentException ()
		{
			var source = new [] { "eagle", "deer", "cat", "dog" };
			source.ToDictionary (s => s.Length);
		}

		[Test]
		public void ToDictionary_KeySelectorArg_ValidArguments_KeySelectorIsUsedForKeysInDictionary ()
		{
			var source = Read (new [] { "1", "2", "3" });
			var result = source.ToDictionary (s => int.Parse (s));
			int check = 1;
			foreach (var pair in result) {
				Assert.That (pair.Key, Is.EqualTo (check));
				Assert.That (pair.Value, Is.EqualTo (check.ToString ()));
				check++;
			}
			Assert.That (check, Is.EqualTo (4));
		}

		[Test]
		public void ToDictionary_KeySelectorArgElementSelectorArg_IntsFromOneToTen_KeySelectorAndElementSelectorAreUsedForDictionaryElements ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
			var result = source.ToDictionary (i => i.ToString (), i => Math.Sqrt (double.Parse (i.ToString ())));
			int check = 1;
			foreach (var pair in result) {
				Assert.That (pair.Key, Is.EqualTo (check.ToString ()));
				Assert.That (pair.Value, Is.EqualTo (Math.Sqrt (double.Parse (check.ToString ()))).Within (0.00001));
				check++;
			}
		}

		[Test]
		public void ToList_IntsFromOneToTen_ReturnsListOfIntsContainingAllElements ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
			var result = source.ToList ();
			Assert.That (result, Is.TypeOf (typeof (List<int>)));
			result.AssertEquals (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
		}

		[Test]
		public void ToLookup_KeySelectorArg_Strings_ReturnsLookupArrayWithStringLengthAsKey ()
		{
			var source = Read (new [] { "eagle", "dog", "cat", "bird", "camel" });
			var result = source.ToLookup (s => s.Length);

			result [3].AssertEquals ("dog", "cat");
			result [4].AssertEquals ("bird");
			result [5].AssertEquals ("eagle", "camel");
		}

		[Test]
		public void ToLookup_KeySelectorArgElementSelectorArg_Strings_ElementSelectorIsUsed ()
		{
			var source = Read (new [] { "eagle", "dog", "cat", "bird", "camel" });
			var result = source.ToLookup (s => s.Length, str => str.ToCharArray ().Reverse ());
			var enumerator = result [3].GetEnumerator ();
			enumerator.MoveNext (); Assert.That (enumerator.Current.ToString (), Is.EqualTo ("dog".ToCharArray ().Reverse ().ToString ()));
			enumerator.MoveNext (); Assert.That (enumerator.Current.ToString (), Is.EqualTo ("cat".ToCharArray ().Reverse ().ToString ()));
			Assert.That (enumerator.MoveNext (), Is.False);

			enumerator = result [4].GetEnumerator ();
			enumerator.MoveNext (); Assert.That (enumerator.Current.ToString (), Is.EqualTo ("bird".ToCharArray ().Reverse ().ToString ()));
			Assert.That (enumerator.MoveNext (), Is.False);

			enumerator = result [5].GetEnumerator ();
			enumerator.MoveNext (); Assert.That (enumerator.Current.ToString (), Is.EqualTo ("eagle".ToCharArray ().Reverse ().ToString ()));
			enumerator.MoveNext (); Assert.That (enumerator.Current.ToString (), Is.EqualTo ("camel".ToCharArray ().Reverse ().ToString ()));
			Assert.That (enumerator.MoveNext (), Is.False);
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Union_SecondArg_PassNullAsArgument_ThrowsArgumentNullException ()
		{
			Read<object> ().Union (null);
		}

		[Test]
		public void Union_SecondArg_ValidIntArguments_NoDuplicatesAndInSourceOrder ()
		{
			var source = Read (new [] { 5, 3, 9, 7, 5, 9, 3, 7 });
			var argument = Read (new [] { 8, 3, 6, 4, 4, 9, 1, 0 });
			source.Union (argument).AssertEquals (5, 3, 9, 7, 8, 6, 4, 1, 0);
		}

		[Test]
		public void Union_SecondArgComparerArg_UpperCaseAndLowerCaseStrings_PassedComparerIsUsed ()
		{
			var source = Read (new [] { "A", "B", "C", "D", "E", "F" });
			var argument = Read (new [] { "a", "b", "c", "d", "e", "f" });
			source.Union (argument, StringComparer.CurrentCultureIgnoreCase).AssertEquals ("A", "B", "C", "D", "E", "F");
		}

		[Test]
		[ExpectedException (typeof (ArgumentNullException))]
		public void Where_NullPredicate_ThrowsArgumentNullException ()
		{
			Read<object> ().Where ((Func<object, bool>) null);
		}

		[Test]
		public void Where_IntegersWithEvensPredicate_YieldsEvenIntegers ()
		{
			var source = Read (new [] { 1, 2, 3, 4, 5 });
			source.Where (i => i % 2 == 0).AssertEquals (2, 4);
		}

		[Test]
		public void Where_StringsWithEvenIndexPredicate_YieldsElementsWithEvenIndex ()
		{
			var source = Read (new [] { "Camel", "Marlboro", "Parisienne", "Lucky Strike" });
			source.Where ((s, i) => i % 2 == 0).AssertEquals ("Camel", "Parisienne");
		}

		[Test]
		public void AsEnumerable_NonNullSource_ReturnsSourceReference ()
		{
			var source = new object [0];
			Assert.That (Enumerable.AsEnumerable (source), Is.SameAs (source));
		}

		[Test]
		public void AsEnumerable_NullSource_ReturnsNull ()
		{
			Assert.That (Enumerable.AsEnumerable<object> (null), Is.Null);
		}

		private Reader<T> Read<T> (params T [] source)
		{
			Debug.Assert (source != null);

			var reader = new Reader<T> (source);

			//
			// If the calling test method is not expecting an exception
			// then check that the source enumerator will be disposed
			// by the time the test is torn.
			//

			var disposed = false;
			var enumerated = false;
			reader.Disposed += delegate { disposed = true; };
			reader.Enumerated += delegate { enumerated = true; };
			AssertionHandler assertion = () => Assert.That (!enumerated || disposed, Is.True, "Enumerator not disposed.");
			tearDownAssertions = (AssertionHandler) Delegate.Combine (tearDownAssertions, assertion);

			return reader;
		}
	}

	[Serializable]
	internal sealed class NonEnumerableList<T> : List<T>, IEnumerable<T> {
		public NonEnumerableList () { }

		public NonEnumerableList (IEnumerable<T> collection) :
			base (collection) { }

		// Re-implement GetEnumerator to be undefined.

		IEnumerator<T> IEnumerable<T>.GetEnumerator ()
		{
			throw new NotImplementedException ();
		}

		IEnumerator IEnumerable.GetEnumerator ()
		{
			return ((IEnumerable<T>) this).GetEnumerator ();
		}
	}

	internal sealed class Reader<T> : IEnumerable<T>, IEnumerator<T> {
		public event EventHandler Disposed;
		public event EventHandler Enumerated;

		private IEnumerable<T> source;
		private IEnumerator<T> cursor;

		public Reader (IEnumerable<T> values)
		{
			Debug.Assert (values != null);
			source = values;
		}

		private IEnumerator<T> Enumerator
		{
			get
			{
				if (cursor == null)
					GetEnumerator ();
				return this;
			}
		}

		public object EOF
		{
			get { return Enumerator.MoveNext (); }
		}

		public IEnumerator<T> GetEnumerator ()
		{
			if (source == null) throw new Exception ("A LINQ Operator called GetEnumerator() twice.");
			cursor = source.GetEnumerator ();
			source = null;

			var handler = Enumerated;
			if (handler != null)
				handler (this, EventArgs.Empty);

			return this;
		}

		IEnumerator IEnumerable.GetEnumerator ()
		{
			return GetEnumerator ();
		}

		public T Read ()
		{
			if (!Enumerator.MoveNext ())
				throw new InvalidOperationException ("No more elements in the source sequence.");
			return Enumerator.Current;
		}

		void IDisposable.Dispose ()
		{
			source = null;
			var e = cursor;
			cursor = null;

			if (e != null) {
				e.Dispose ();

				var handler = Disposed;
				if (handler != null)
					handler (this, EventArgs.Empty);
			}
		}

		private IEnumerator<T> GetSourceEnumerator ()
		{
			if (source != null && cursor == null)
				throw new InvalidOperationException (/* GetEnumerator not called yet */);
			if (source == null && cursor == null)
				throw new ObjectDisposedException (GetType ().FullName);

			return cursor;
		}

		bool IEnumerator.MoveNext ()
		{
			return GetSourceEnumerator ().MoveNext ();
		}

		void IEnumerator.Reset ()
		{
			GetSourceEnumerator ().Reset ();
		}

		T IEnumerator<T>.Current
		{
			get { return GetSourceEnumerator ().Current; }
		}

		object IEnumerator.Current
		{
			get { return ((IEnumerator<T>) this).Current; }
		}
	}

	internal static class ReaderTestExtensions {
		public static void AssertEnded<T> (this Reader<T> reader)
		{
			Debug.Assert (reader != null);

			Assert.That (reader.EOF, Is.False, "Too many elements in source.");
		}

		public static Reader<T> AssertNext<T> (this Reader<T> reader, Constraint constraint)
		{
			Debug.Assert (reader != null);
			Debug.Assert (constraint != null);

			Assert.That (reader.Read (), constraint);
			return reader;
		}
	}

	internal static class Tester {
		public static void AssertEquals<T> (this IEnumerable<T> actuals, params T [] expectations)
		{
			using (var e = actuals.GetEnumerator ()) {
				foreach (var expected in expectations) {
					e.MoveNext ();
					Assert.That (e.Current, Is.EqualTo (expected));
				}

				Assert.That (e.MoveNext (), Is.False);
			}
		}
	}
}