diff --git a/lib/xlsxtream/io/rubyzip.rb b/lib/xlsxtream/io/rubyzip.rb
index f706366..f60ef4f 100644
--- a/lib/xlsxtream/io/rubyzip.rb
+++ b/lib/xlsxtream/io/rubyzip.rb
@@ -1,12 +1,16 @@
 require "zip"
+require "xlsxtream/errors"
 
 module Xlsxtream
   module IO
     class RubyZip
-      def initialize(path_or_io)
-        @stream = path_or_io.respond_to? :reopen
-        path_or_io.binmode if path_or_io.respond_to? :binmode
-        @zos = Zip::OutputStream.new(path_or_io, @stream)
+      def initialize(io)
+        unless io.respond_to? :pos and io.respond_to? :pos=
+          raise Error, 'IO is not seekable'
+        end
+        io.binmode if io.respond_to? :binmode
+        stream = true
+        @zos = Zip::OutputStream.new(io, stream)
       end
 
       def <<(data)
@@ -20,7 +24,6 @@ def add_file(path)
       def close
         os = @zos.close_buffer
         os.flush if os.respond_to? :flush
-        os.close if !@stream and os.respond_to? :close
       end
     end
   end
diff --git a/lib/xlsxtream/workbook.rb b/lib/xlsxtream/workbook.rb
index 0c6cd31..d948a5b 100644
--- a/lib/xlsxtream/workbook.rb
+++ b/lib/xlsxtream/workbook.rb
@@ -1,12 +1,9 @@
 # encoding: utf-8
-require "stringio"
 require "xlsxtream/errors"
 require "xlsxtream/xml"
 require "xlsxtream/shared_string_table"
 require "xlsxtream/workbook"
 require "xlsxtream/io/rubyzip"
-require "xlsxtream/io/directory"
-require "xlsxtream/io/stream"
 
 module Xlsxtream
   class Workbook
@@ -22,8 +19,8 @@ class Workbook
 
     class << self
 
-      def open(data = nil, options = {})
-        workbook = new(data, options)
+      def open(output = nil, options = {})
+        workbook = new(output, options)
         if block_given?
           begin
             yield workbook
@@ -37,10 +34,16 @@ def open(data = nil, options = {})
 
     end
 
-    def initialize(data = nil, options = {})
+    def initialize(output = nil, options = {})
+      output ||= StringIO.new
       @options = options
       io_wrapper = options[:io_wrapper] || IO::RubyZip
-      @io = io_wrapper.new(data || StringIO.new)
+      if output.is_a?(String) || !output.respond_to?(:<<)
+        @file = File.open(output, 'wb')
+        @io = io_wrapper.new(@file)
+      else
+        @io = io_wrapper.new(output)
+      end
       @sst = SharedStringTable.new
       @worksheets = Hash.new { |hash, name| hash[name] = hash.size + 1 }
     end
@@ -74,6 +77,7 @@ def close
       write_root_rels
       write_content_types
       @io.close
+      @file.close if @file
       nil
     end
 
diff --git a/test/xlsxtream/io/directory_test.rb b/test/xlsxtream/io/directory_test.rb
new file mode 100644
index 0000000..6c96c2e
--- /dev/null
+++ b/test/xlsxtream/io/directory_test.rb
@@ -0,0 +1,32 @@
+require 'test_helper'
+require 'xlsxtream/io/directory'
+require 'pathname'
+
+module Xlsxtream
+  module IO
+    class DirectoryTest < Minitest::Test
+
+      def test_writes_of_multiple_files
+        Dir.mktmpdir do |dir|
+          io = Xlsxtream::IO::Directory.new(dir)
+          io.add_file("book1.xml")
+          io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />'
+          io.add_file("book2.xml")
+          io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook>'
+          io << '</workbook>'
+          io.add_file("empty.txt")
+          io.add_file("another.xml")
+          io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />'
+          io.close
+
+          dir = Pathname(dir)
+          assert_equal '', dir.join('empty.txt').read
+          assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />', dir.join('book1.xml').read
+          assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook></workbook>', dir.join('book2.xml').read
+          assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />', dir.join('another.xml').read
+        end
+
+      end
+    end
+  end
+end
diff --git a/test/xlsxtream/io/hash_test.rb b/test/xlsxtream/io/hash_test.rb
new file mode 100644
index 0000000..efbd17d
--- /dev/null
+++ b/test/xlsxtream/io/hash_test.rb
@@ -0,0 +1,30 @@
+require 'test_helper'
+require 'xlsxtream/io/hash'
+
+module Xlsxtream
+  module IO
+    class HashTest < Minitest::Test
+
+      def test_writes_of_multiple_files
+        buffer = StringIO.new
+
+        io = Xlsxtream::IO::Hash.new(buffer)
+        io.add_file("book1.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />'
+        io.add_file("book2.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook>'
+        io << '</workbook>'
+        io.add_file("empty.txt")
+        io.add_file("another.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />'
+        io.close
+
+        file_contents = io.to_h
+        assert_equal '', file_contents['empty.txt']
+        assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />', file_contents['book1.xml']
+        assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook></workbook>', file_contents['book2.xml']
+        assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />', file_contents['another.xml']
+      end
+    end
+  end
+end
diff --git a/test/xlsxtream/io/rubyzip_test.rb b/test/xlsxtream/io/rubyzip_test.rb
new file mode 100644
index 0000000..be8666c
--- /dev/null
+++ b/test/xlsxtream/io/rubyzip_test.rb
@@ -0,0 +1,40 @@
+require 'test_helper'
+require 'xlsxtream/io/rubyzip'
+require 'zip'
+
+module Xlsxtream
+  module IO
+    class RubyZipTest < Minitest::Test
+
+      def test_writes_of_multiple_files
+        zip_buf = Tempfile.new('ztio-test')
+
+        io = Xlsxtream::IO::RubyZip.new(zip_buf)
+        io.add_file("book1.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />'
+        io.add_file("book2.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook>'
+        io << '</workbook>'
+        io.add_file("empty.txt")
+        io.add_file("another.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />'
+        io.close
+
+        zip_buf.rewind
+
+        file_contents = {}
+        ::Zip::File.open(zip_buf) do |zip_file|
+          zip_file.each do |entry|
+            file_contents[entry.name] = entry.get_input_stream.read
+          end
+        end
+        assert_equal '', file_contents['empty.txt']
+        assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />', file_contents['book1.xml']
+        assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook></workbook>', file_contents['book2.xml']
+        assert_equal '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />', file_contents['another.xml']
+      ensure
+        zip_buf.close! if zip_buf
+      end
+    end
+  end
+end
diff --git a/test/xlsxtream/io/stream_test.rb b/test/xlsxtream/io/stream_test.rb
new file mode 100644
index 0000000..aa756ed
--- /dev/null
+++ b/test/xlsxtream/io/stream_test.rb
@@ -0,0 +1,36 @@
+require 'test_helper'
+require 'xlsxtream/io/stream'
+
+module Xlsxtream
+  module IO
+    class StreamTest < Minitest::Test
+
+      def test_writes_of_multiple_files
+        buffer = StringIO.new
+
+        io = Xlsxtream::IO::Stream.new(buffer)
+        io.add_file("book1.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />'
+        io.add_file("book2.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook>'
+        io << '</workbook>'
+        io.add_file("empty.txt")
+        io.add_file("another.xml")
+        io << '<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />'
+        io.close
+
+        file_contents = buffer.string
+        assert_equal <<-EOF, file_contents
+book1.xml
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook />
+book2.xml
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?><workbook></workbook>
+empty.txt
+
+another.xml
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?><another />
+EOF
+      end
+    end
+  end
+end
diff --git a/test/xlsxtream/workbook_test.rb b/test/xlsxtream/workbook_test.rb
index d5ce02a..460ea98 100644
--- a/test/xlsxtream/workbook_test.rb
+++ b/test/xlsxtream/workbook_test.rb
@@ -1,10 +1,27 @@
 require 'test_helper'
+require 'tempfile'
 require 'xlsxtream/workbook'
 require 'xlsxtream/io/hash'
 
 module Xlsxtream
   class WorksheetTest < Minitest::Test
 
+    def test_workbook_from_path
+      tempfile = Tempfile.new('xlsxtream')
+      Workbook.open(tempfile.path) {}
+      refute_equal 0, tempfile.size
+    ensure
+      tempfile.close! if tempfile
+    end
+
+    def test_workbook_from_io
+      tempfile = Tempfile.new('xlsxtream')
+      Workbook.open(tempfile) {}
+      refute_equal 0, tempfile.size
+    ensure
+      tempfile.close! if tempfile
+    end
+
     def test_empty_workbook
       iow_spy = io_wrapper_spy
       Workbook.open(nil, :io_wrapper => iow_spy) {}