Add binary mode. Resolves Github #13

lib/fakefs/file.rb

@@ -196,6 +196,8 @@ module FakeFS
       @file = FileSystem.find(path)
       @open = true
 
+      check_modes!
+
       file_creation_mode? ? create_missing_file : check_file_existence!
 
       @stream = StringIO.new(@file.content, mode)
@@ -231,6 +233,10 @@ module FakeFS
 
   private
 
+    def check_modes!
+      StringIO.new("", @mode)
+    end
+
     def check_file_existence!
       unless @file
         raise Errno::ENOENT, "No such file or directory - #{@file}"
@@ -242,7 +248,7 @@ module FakeFS
     end
 
     def mode_in?(list)
-      list.include?(@mode)
+      list.any? { |element| @mode.include?(element) }
     end
 
     def create_missing_file

test/fakefs_test.rb

@@ -214,6 +214,17 @@ class FakeFSTest < Test::Unit::TestCase
     assert_equal 'Yada Yada', File.read(path)
   end
 
+  def test_raises_error_when_opening_with_binary_mode_only
+    assert_raise ArgumentError do
+      File.open("/foo", "b")
+    end
+  end
+
+  def test_can_open_file_in_binary_mode
+    File.open("/foo", "wb") { |x| x << "a" }
+    assert_equal "a", File.read("/foo")
+  end
+
   def test_can_chunk_io_when_reading
     path = '/path/to/file.txt'
     File.open(path, 'w') do |f|