Added LastOrDefault method and tests.

ShittyLINQ/LastOrDefault.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace ShittyLINQ
+{
+  public static partial class Extensions
+  {
+    public static T LastOrDefault<T>(this IEnumerable<T> self)
+    {
+      if (self == null) throw new ArgumentNullException(nameof(self));
+
+      var iterator = self.GetEnumerator();
+
+      if (iterator.MoveNext())
+      {
+        T result;
+        do
+        {
+          result = iterator.Current;
+        }
+        while (iterator.MoveNext());
+        return result;
+      }
+      return default(T);
+    }
+
+    public static T LastOrDefault<T>(this IEnumerable<T> self, Func<T, bool> predicate)
+    {
+      if (self == null || predicate == null) throw new ArgumentNullException(nameof(self));
+
+      self = self.Where(predicate);
+
+      var iterator = self.GetEnumerator();
+      if (iterator.MoveNext())
+      {
+        T result;
+        do
+        {
+          result = iterator.Current;
+        }
+        while (iterator.MoveNext());
+        return result;
+      }
+      return default(T);
+    }
+  }
+}

ShittyLinqTests/LastOrDefaultTests.cs

@@ -0,0 +1,96 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using ShittyLINQ;
+using System;
+namespace ShittyTests
+{
+  [TestClass]
+  public class LastOrDefaultTests
+  {
+    [TestMethod]
+    public void LastOrDefault_GetLastNumber()
+    {
+      int[] numbers = new int[] { 1, 2, 3, 4, 5 };
+      int expectedResult = 5;
+
+      int result = numbers.LastOrDefault();
+
+      Assert.AreEqual(expectedResult, result);
+    }
+
+    [TestMethod]
+    public void LastOrDefault_GetLastNumberMatchingPredicate()
+    {
+      int[] numbers = new int[] { 1, 2, 3, 4, 5 };
+      int expectedResult = 3;
+      bool predicate(int i) => i == 3;
+
+      int result = numbers.LastOrDefault(predicate);
+
+      Assert.AreEqual(expectedResult, result);
+    }
+
+    [TestMethod]
+    [ExpectedException(typeof(ArgumentNullException))]
+    public void LastOrDefault_SourceIsNull()
+    {
+      int[] numbers = null;
+
+      int result = numbers.LastOrDefault();
+    }
+
+    [TestMethod]
+    [ExpectedException(typeof(ArgumentNullException))]
+    public void LastOrDefault_SourceIsNullWithPredicate()
+    {
+      int[] numbers = null;
+      bool predicate(int i) => i == 3;
+
+      int result = numbers.LastOrDefault(predicate);
+    }
+
+    [TestMethod]
+    [ExpectedException(typeof(ArgumentNullException))]
+    public void LastOrDefault_PredicateIsNull()
+    {
+      int[] numbers = new int[] { 1, 2, 3, 4, 5 };
+      Func<int, bool> predicate = null;
+
+      int result = numbers.LastOrDefault(predicate);
+    }
+
+    [TestMethod]
+    public void LastOrDefault_SourceIsEmpty()
+    {
+      int[] numbers = new int[] { };
+      int expectedResult = default(int);
+
+      int result = numbers.LastOrDefault();
+
+      Assert.AreEqual(expectedResult, result);
+    }
+
+    [TestMethod]
+    public void LastOrDefault_SourceIsEmptyWithPredicate()
+    {
+      int[] numbers = new int[] { };
+      bool predicate(int i) => i == 3;
+      int expectedResult = default(int);
+
+      int result = numbers.LastOrDefault(predicate);
+
+      Assert.AreEqual(expectedResult, result);
+    }
+
+    [TestMethod]
+    public void LastOrDefault_NoElementMatchesPredicate()
+    {
+      int[] numbers = new int[] { 1, 2, 4, 5 };
+      bool predicate(int i) => i == 3;
+      int expectedResult = default(int);
+
+      int result = numbers.LastOrDefault(predicate);
+
+      Assert.AreEqual(expectedResult, result);
+    }
+  }
+}