Add Average extension method and tests

ShittyLINQ/Average.cs

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+using System;
+using System.Collections.Generic;
+
+namespace ShittyLINQ
+{
+    public static partial class Extensions
+    {
+        /// <summary>
+        /// Calculates the average nummeric value
+        /// of an IEnumerable collection.
+        /// </summary>
+        private static R Average<R, T>(this IEnumerable<T> self)
+        {
+            if (self == null)
+            {
+                throw new ArgumentNullException();
+            }
+
+            dynamic sum = default(R);
+            int count = 0;
+
+            foreach (var number in self)
+            {
+                sum += number;
+                count++;
+            }
+
+            if (count == 0)
+            {
+                throw new InvalidOperationException("The sequence is empty.");
+            }
+
+            return sum / count;
+        }
+
+        public static double Average(this IEnumerable<int> self)
+        {
+            return self.Average<double, int>();
+        }
+
+        public static float Average(this IEnumerable<float> self)
+        {
+            return self.Average<float, float>();
+        }
+
+        public static double Average(this IEnumerable<double> self)
+        {
+            return self.Average<double, double>();
+        }
+
+        public static double Average(this IEnumerable<long> self)
+        {
+            return self.Average<double, long>();
+        }
+    }
+}

ShittyLinqTests/AverageTests.cs

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+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using ShittyLINQ;
+using System;
+
+namespace ShittyTests
+{
+    [TestClass]
+    public class AverageTests
+    {
+        [TestMethod]
+        public void Ints()
+        {
+            int[] numbers = new int[] { 0, 7, 4, 1 };
+            double expectedResult = 3d;
+            double actualResult = numbers.Average();
+
+            Assert.AreEqual(expectedResult, actualResult);
+        }
+
+        [TestMethod]
+        public void Floats()
+        {
+            float[] numbers = new float[] { 3.5f, -4f, 14f, 7f };
+            float expectedResult = 5.125f;
+            float actualResult = numbers.Average();
+
+            Assert.AreEqual(expectedResult, actualResult);
+        }
+
+        [TestMethod]
+        public void Doubles()
+        {
+            double[] numbers = new double[] { -1.25d, 2.75d, 7.5d, -4d };
+            double expectedResult = 1.25d;
+            double actualResult = numbers.Average();
+
+            Assert.AreEqual(expectedResult, actualResult);
+        }
+
+        [TestMethod]
+        public void Longs()
+        {
+            long[] numbers = new long[] { 5, 3, 17, 1 };
+            double expectedResult = 6.5d;
+            double actualResult = numbers.Average();
+
+            Assert.AreEqual(expectedResult, actualResult);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void CollectionIsEmpty()
+        {
+            int[] numbers = new int[] { };
+            numbers.Average();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentNullException))]
+        public void CollectionIsNull()
+        {
+            int[] numbers = null;
+            numbers.Average();
+        }
+    }
+}