diff --git a/lib/fakefs.rb b/lib/fakefs.rb
index e1b2d34..5d8d535 100644
--- a/lib/fakefs.rb
+++ b/lib/fakefs.rb
@@ -1,4 +1,6 @@
-module FakeFS
+require 'fileutils'
+
+class FakeFS
   module FileUtils
     extend self
 
@@ -41,13 +43,17 @@ module FakeFS
     end
 
     def self.expand_path(path)
-      ::File.expand_path(path)
+      RealFile.expand_path(path)
     end
 
     def self.readlink(path)
       symlink = FileSystem.find(path)
       FileSystem.find(symlink.target).to_s
     end
+
+    def self.dirname(path)
+      RealFile.dirname(path)
+    end
   end
 
   class Dir
@@ -60,54 +66,6 @@ module FakeFS
     end
   end
 
-  module FileSystem
-    extend self
-
-    def fs
-      @fs ||= MockDir.new('.')
-    end
-
-    def clear
-      @fs = nil
-    end
-
-    def find(path)
-      parts = path_parts(path)
-
-      target = parts[0...-1].inject(fs) do |dir, part|
-        dir[part] || {}
-      end
-
-      case parts.last
-      when '*'
-        target.values
-      else
-        target[parts.last]
-      end
-    end
-
-    def add(path, object)
-      parts = path_parts(path)
-
-      d = parts[0...-1].inject(fs) do |dir, part|
-        dir[part] ||= MockDir.new(part, dir)
-      end
-
-      object.name = parts.last
-      object.parent = d
-      d[parts.last] = object
-    end
-
-    def delete(path)
-      if dir = FileSystem.find(path)
-        dir.parent.delete(dir.name)
-      end
-    end
-
-    def path_parts(path)
-      path.split(File::PATH_SEPARATOR)
-    end
-  end
 
   class MockDir < Hash
     attr_accessor :name, :parent
@@ -117,6 +75,10 @@ module FakeFS
       @parent = parent
     end
 
+    def files
+      values
+    end
+
     def entry
       self
     end
@@ -150,8 +112,63 @@ module FakeFS
       entry.send(*args, &block)
     end
   end
+
+  def fs
+    @fs ||= MockDir.new('.')
+  end
+
+  def clear
+    @fs = nil
+  end
+
+  def find(path)
+    parts = path_parts(path)
+
+    target = parts[0...-1].inject(fs) do |dir, part|
+      dir[part] || {}
+    end
+
+    case parts.last
+    when '*'
+      target.values
+    else
+      target[parts.last]
+    end
+  end
+
+  def add(path, object)
+    parts = path_parts(path)
+
+    d = parts[0...-1].inject(fs) do |dir, part|
+      dir[part] ||= MockDir.new(part, dir)
+    end
+
+    object.name = parts.last
+    object.parent = d
+    d[parts.last] = object
+  end
+
+  def delete(path)
+    if dir = FileSystem.find(path)
+      dir.parent.delete(dir.name)
+    end
+  end
+
+  def path_parts(path)
+    path.split(File::PATH_SEPARATOR)
+  end
+
+  def method_missing(*args, &block)
+    fs.send(*args, &block)
+  end
+
+  FileSystem = FakeFS.new('.')
 end
 
+RealFile = File
+RealFileUtils = FileUtils
+RealDir = Dir
+
 Object.class_eval do
   remove_const(:Dir)
   remove_const(:File)
diff --git a/test/fake_fs.rb b/test/fake_fs.rb
new file mode 100644
index 0000000..d3fe3ec
--- /dev/null
+++ b/test/fake_fs.rb
@@ -0,0 +1,15 @@
+$LOAD_PATH.unshift File.join(File.dirname(__FILE__), '..', 'lib')
+require 'fakefs'
+require 'test/unit'
+
+class FakeFSTest < Test::Unit::TestCase
+  def test_can_be_initialized_empty
+    fs = FakeFS.new('.')
+    assert_equal 0, fs.files.size
+  end
+
+  def test_can_be_initialized_with_an_existing_directory
+    fs = FakeFS.new(File.expand_path(File.dirname(__FILE__)))
+    assert_equal 1, fs.files.size
+  end
+end