Added CurrentDirectory extension

Author: gigi81

src/System.IO.Abstractions.Extensions/IFileSystemExtensions.cs

@@ -0,0 +1,15 @@
+namespace System.IO.Abstractions.Extensions
+{
+    public static class IFileSystemExtensions
+    {
+        /// <summary>
+        /// Get the current directory for the specified <paramref name="fileSystem"/>
+        /// </summary>
+        /// <param name="fileSystem">FileSystem in use</param>
+        /// <returns>An <see cref="IDirectoryInfo"/> for the current directory</returns>
+        public static IDirectoryInfo CurrentDirectory(this FileSystem fileSystem)
+        {
+            return fileSystem.DirectoryInfo.FromDirectoryName(fileSystem.Directory.GetCurrentDirectory());
+        }
+    }
+}

tests/System.IO.Abstractions.Extensions.Tests/FileSystemExtensionsTests.cs

@@ -0,0 +1,18 @@
+using NUnit.Framework;
+
+namespace System.IO.Abstractions.Extensions.Tests
+{
+    [TestFixture]
+    public class FileSystemExtensionsTests
+    {
+        [Test]
+        public void CurrentDirectoryTest()
+        {
+            var fs = new FileSystem();
+            var fullName = fs.CurrentDirectory().FullName;
+
+            Assert.IsFalse(String.IsNullOrWhiteSpace(fullName));
+            Assert.AreEqual(Environment.CurrentDirectory, fullName);
+        }
+    }
+}