Raise an IOError when a file is read in a write-only mode.

lib/fakefs/file.rb

@@ -116,7 +116,8 @@ module FakeFS
     end
 
     def read
-      raise IOError.new('closed stream') unless @open
+      raise IOError, 'closed stream' unless @open
+      raise IOError, 'not opened for reading' if write_only?
       @file.content
     end
 
@@ -172,5 +173,9 @@ module FakeFS
         @file = FileSystem.add(path, FakeFile.new)
       end
     end
+
+    def write_only?
+      @mode == WRITE_ONLY || @mode == APPEND_WRITE_ONLY
+    end
   end
 end

test/fakefs_test.rb

@@ -146,6 +146,26 @@ class FakeFSTest < Test::Unit::TestCase
     assert File.exists?("foo")
   end
 
+  def test_file_in_write_only_raises_error_when_reading
+    FileUtils.touch("foo")
+
+    f = File.open("foo", "w")
+
+    assert_raises(IOError) do
+      f.read
+    end
+  end
+
+  def test_file_in_append_write_only_raises_error_when_reading
+    FileUtils.touch("foo")
+
+    f = File.open("foo", "a")
+
+    assert_raises(IOError) do
+      f.read
+    end
+  end
+
   def test_can_read_files_once_written
     path = '/path/to/file.txt'
     File.open(path, 'w') do |f|