```ruby
require File.expand_path('../../../../spec_helper', __FILE__)
require 'stringio'
require 'zlib'

describe 'Zlib::GzipFile#close' do
  it 'finishes the stream and closes the io' do
    io = StringIO.new
    Zlib::GzipWriter.wrap io do |gzio|
      gzio.close

      gzio.closed?.should == true

      lambda { gzio.orig_name }.should \
        raise_error(Zlib::GzipFile::Error, 'closed gzip stream')
      lambda { gzio.comment }.should \
        raise_error(Zlib::GzipFile::Error, 'closed gzip stream')
    end

    io.string[10..-1].should == "\003\000\000\000\000\000\000\000\000\000"
  end
end

```

Add magic comment and give initial string to set its encoding.
user
```ruby
# -*- encoding: ascii-8bit -*-
require File.expand_path('../../../../spec_helper', __FILE__)
require 'stringio'
require 'zlib'

describe 'Zlib::GzipFile#close' do
  it 'finishes the stream and closes the io' do
    io = StringIO.new ""
    Zlib::GzipWriter.wrap io do |gzio|
      gzio.close

      gzio.closed?.should == true

      lambda { gzio.orig_name }.should \
        raise_error(Zlib::GzipFile::Error, 'closed gzip stream')
      lambda { gzio.comment }.should \
        raise_error(Zlib::GzipFile::Error, 'closed gzip stream')
    end

    io.string[10..-1].should == "\003\000\000\000\000\000\000\000\000\000"
  end
end

```
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