Add Intersect method and tests #47

ShittyLINQ/Intersect.cs

@@ -0,0 +1,32 @@
+namespace ShittyLINQ
+{
+    using System;
+    using System.Collections.Generic;
+
+    public static partial class Extensions
+    {
+        public static IEnumerable<T> Intersect<T>(this IEnumerable<T> self, IEnumerable<T> second)
+        {
+            return Intersect(self, second, EqualityComparer<T>.Default);
+        }
+
+        public static IEnumerable<T> Intersect<T>(this IEnumerable<T> self, IEnumerable<T> second, IEqualityComparer<T> comparer)
+        {
+            if (self == null)
+                throw new ArgumentNullException(nameof(self));
+            if (second == null)
+                throw new ArgumentNullException(nameof(second));
+
+            foreach (var item in self)
+            {
+                foreach (var secondItem in second)
+                {
+                    if (comparer.Equals(item, secondItem))
+                    {
+                        yield return item;
+                    }
+                }
+            }
+        }
+    }
+}

ShittyLinqTests/IntersectTests.cs

@@ -0,0 +1,58 @@
+namespace ShittyTests
+{
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+    using ShittyLINQ;
+    using ShittyTests.TestHelpers;
+
+    [TestClass]
+    public class IntersectTests
+    {
+        [TestMethod]
+        public void Intersect_ReturnsExpected()
+        {
+            var first = new[] { 1, 2, 3, 4, 5 };
+            var second = new[] { 1, 2, 5, 6, 7 };
+            var expectedResult = new[] { 1, 2, 5 };
+
+            var result = first.Intersect(second);
+
+            TestHelper.AssertCollectionsAreSame(expectedResult, result);
+        }
+
+        [TestMethod]
+        public void Intersect_ReturnsExpectedWithFirstCollectionEmpty()
+        {
+            var first = new int[] { };
+            var second = new[] { 1, 2, 5, 6, 7 };
+            var expectedResult = new int[] { };
+
+            var result = first.Intersect(second);
+
+            TestHelper.AssertCollectionsAreSame(expectedResult, result);
+        }
+
+        [TestMethod]
+        public void Intersect_ReturnsExpectedWithSecondCollectionEmpty()
+        {
+            var first = new[] { 1, 2, 3, 4, 5 };
+            var second = new int[] { };
+            var expectedResult = new int[] { };
+
+            var result = first.Intersect(second);
+
+            TestHelper.AssertCollectionsAreSame(expectedResult, result);
+        }
+
+        [TestMethod]
+        public void Intersect_ReturnsExpectedWithoutCommonValue()
+        {
+            var first = new[] { 1, 2, 3, 4, 5 };
+            var second = new int[] { 6, 7, 8, 9, 10 };
+            var expectedResult = new int[] { };
+
+            var result = first.Intersect(second);
+
+            TestHelper.AssertCollectionsAreSame(expectedResult, result);
+        }
+    }
+}