diff --git a/core/io/copy_stream_spec.rb b/core/io/copy_stream_spec.rb
index dd8b201dc8..9148770c1e 100644
--- a/core/io/copy_stream_spec.rb
+++ b/core/io/copy_stream_spec.rb
@@ -1,50 +1,184 @@
 require File.expand_path('../../../spec_helper', __FILE__)
+require File.expand_path('../fixtures/classes', __FILE__)
 
 ruby_version_is "1.9" do
-  describe "IO.copy_stream" do
-    it "needs to be reviewed for spec completeness"
+  describe :io_copy_stream_to_file, :shared => true do
+    it "copies the entire IO contents to the file" do
+      IO.copy_stream(@object.from, @to_name)
+      @to_name.should have_data(@content)
+    end
+
+    it "returns the number of bytes copied" do
+      IO.copy_stream(@object.from, @to_name).should == @size
+    end
+
+    it "copies only length bytes when specified" do
+      IO.copy_stream(@object.from, @to_name, 8).should == 8
+      @to_name.should have_data("Line one")
+    end
+
+    it "copies only length bytes from the offset" do
+      IO.copy_stream(@object.from, @to_name, 8, 4).should == 8
+      @to_name.should have_data(" one\n\nLi")
+    end
+
+    it "calls #to_path to convert on object to a file name" do
+      obj = mock("io_copy_stream_to")
+      obj.should_receive(:to_path).and_return(@to_name)
+
+      IO.copy_stream(@object.from, obj)
+      @to_name.should have_data(@content)
+    end
+
+    it "raises a TypeError if #to_path does not return a String" do
+      obj = mock("io_copy_stream_to")
+      obj.should_receive(:to_path).and_return(1)
+
+      lambda { IO.copy_stream(@object.from, obj) }.should raise_error(TypeError)
+    end
   end
 
-  describe "IO.copy_stream" do
-    before :each do
-      # TODO: multi-line content (esp. on Windows!)
-      @content = "one-two-three"
+  describe :io_copy_stream_to_io, :shared => true do
+    it "copies the entire IO contents to the IO" do
+      IO.copy_stream(@object.from, @to_io)
+      @to_name.should have_data(@content)
+    end
 
-      @filename_src = tmp("source")
-      touch(@filename_src) { |f| f.write(@content) }
-      @io_src = new_io(@filename_src, "rb")
+    it "returns the number of bytes copied" do
+      IO.copy_stream(@object.from, @to_io).should == @size
+    end
 
-      @filename_dest = tmp("destination")
-      # TODO: new_io doesn't work here due to bug in mspsec
-      # @io_dest = new_io(@filename_dest, "w")
-      @io_dest = File.open(@filename_dest, "wb")
+    it "starts writing at the destination IO's current position" do
+      @to_io.write("prelude ")
+      IO.copy_stream(@object.from, @to_io)
+      @to_name.should have_data("prelude " + @content)
     end
 
-    after :each do
-      @io_src.close unless @io_src.closed?
-      @io_dest.close unless @io_dest.closed?
-      File.unlink @filename_src
-      File.unlink @filename_dest
+    it "leaves the destination IO position at the last write" do
+      IO.copy_stream(@object.from, @to_io)
+      @to_io.pos.should == @size
     end
 
-    it "copies from an IO instance to a named file" do
-      IO.copy_stream(@io_src, @filename_dest).should == @content.size
-      File.read(@filename_dest).should == @content
+    it "raises an IOError if the destination IO is not open for writing" do
+      @to_io.close
+      @to_io = File.open @to_name, "r"
+      lambda { IO.copy_stream @object.from, @to_io }.should raise_error(IOError)
     end
 
-    it "copies from a named file to a named file" do
-      IO.copy_stream(@filename_src, @filename_dest).should == @content.size
-      File.read(@filename_dest).should == @content
+    it "does not close the destination IO" do
+      IO.copy_stream(@object.from, @to_io)
+      @to_io.closed?.should be_false
     end
 
-    it "copies from a named file to an IO instance" do
-      IO.copy_stream(@filename_src, @io_dest).should == @content.size
-      File.read(@filename_dest).should == @content
+    it "copies only length bytes when specified" do
+      IO.copy_stream(@object.from, @to_io, 8).should == 8
+      @to_name.should have_data("Line one")
     end
 
-    it "copies from an IO instance to an IO instance" do
-      IO.copy_stream(@io_src, @io_dest).should == @content.size
-      File.read(@filename_dest).should == @content
+    it "copies only length bytes from the offset" do
+      IO.copy_stream(@object.from, @to_io, 8, 4).should == 8
+      @to_name.should have_data(" one\n\nLi")
+    end
+  end
+
+  describe "IO.copy_stream" do
+    before :each do
+      @from_name = fixture __FILE__, "copy_stream.txt"
+      @to_name = tmp("io_copy_stream_io_name")
+
+      @content = IO.read(@from_name)
+      @size = @content.size
+    end
+
+    after :each do
+      rm_r @to_name
+    end
+
+    describe "from an IO" do
+      before :each do
+        @from_io = File.open @from_name, "rb"
+        IOSpecs::CopyStream.from = @from_io
+      end
+
+      after :each do
+        @from_io.close
+      end
+
+      it "raises an IOError if the source IO is not open for reading" do
+        @from_io.close
+        @from_io = File.open @from_name, "a"
+        lambda { IO.copy_stream @from_io, @to_name }.should raise_error(IOError)
+      end
+
+      it "does not close the source IO" do
+        IO.copy_stream(@from_io, @to_name)
+        @from_io.closed?.should be_false
+      end
+
+      it "does not change the IO offset when an offset is specified" do
+        @from_io.pos = 10
+        IO.copy_stream(@from_io, @to_name, 8, 4)
+        @from_io.pos.should == 10
+      end
+
+      it "does change the IO offset when an offset is not specified" do
+        @from_io.pos = 10
+        IO.copy_stream(@from_io, @to_name)
+        @from_io.pos.should == 42
+      end
+
+      describe "to a file name" do
+        it_behaves_like :io_copy_stream_to_file, nil, IOSpecs::CopyStream
+      end
+
+      describe "to an IO" do
+        before :each do
+          @to_io = File.open @to_name, "wb"
+        end
+
+        after :each do
+          @to_io.close
+        end
+
+        it_behaves_like :io_copy_stream_to_io, nil, IOSpecs::CopyStream
+      end
+    end
+
+    describe "from a file name" do
+      before :each do
+        IOSpecs::CopyStream.from = @from_name
+      end
+
+      it "calls #to_path to convert on object to a file name" do
+        obj = mock("io_copy_stream_from")
+        obj.should_receive(:to_path).and_return(@from_name)
+
+        IO.copy_stream(obj, @to_name)
+        @to_name.should have_data(@content)
+      end
+
+      it "raises a TypeError if #to_path does not return a String" do
+        obj = mock("io_copy_stream_from")
+        obj.should_receive(:to_path).and_return(1)
+
+        lambda { IO.copy_stream(obj, @to_name) }.should raise_error(TypeError)
+      end
+
+      describe "to a file name" do
+        it_behaves_like :io_copy_stream_to_file, nil, IOSpecs::CopyStream
+      end
+
+      describe "to an IO" do
+        before :each do
+          @to_io = File.open @to_name, "wb"
+        end
+
+        after :each do
+          @to_io.close
+        end
+
+        it_behaves_like :io_copy_stream_to_io, nil, IOSpecs::CopyStream
+      end
     end
   end
 end
diff --git a/core/io/fixtures/classes.rb b/core/io/fixtures/classes.rb
index 5ff334bdf9..6ac70b5c3e 100644
--- a/core/io/fixtures/classes.rb
+++ b/core/io/fixtures/classes.rb
@@ -74,4 +74,14 @@ def self.closed_io
   def self.io_mock(obj, method, &block)
     obj.singleton_class.send(:define_method, method, &block)
   end
+
+  module CopyStream
+    def self.from=(from)
+      @from = from
+    end
+
+    def self.from
+      @from
+    end
+  end
 end
diff --git a/core/io/fixtures/copy_stream.txt b/core/io/fixtures/copy_stream.txt
new file mode 100644
index 0000000000..a2d827b351
--- /dev/null
+++ b/core/io/fixtures/copy_stream.txt
@@ -0,0 +1,6 @@
+Line one
+
+Line three
+Line four
+
+Line last