Fix IO.copy_stream with a Tempfile destination

* Fixes oracle/truffleruby#3280

Author: eregon

core/io/copy_stream_spec.rb

@@ -69,9 +69,12 @@
   end
 
   it "raises an IOError if the destination IO is not open for writing" do
-    @to_io.close
-    @to_io = new_io @to_name, "r"
-    -> { IO.copy_stream @object.from, @to_io }.should raise_error(IOError)
+    to_io = new_io __FILE__, "r"
+    begin
+      -> { IO.copy_stream @object.from, to_io }.should raise_error(IOError)
+    ensure
+      to_io.close
+    end
   end
 
   it "does not close the destination IO" do
@@ -109,7 +112,8 @@
   end
 
   after :each do
-    rm_r @to_name, @from_bigfile
+    rm_r @to_name if @to_name
+    rm_r @from_bigfile
   end
 
   describe "from an IO" do
@@ -164,6 +168,25 @@
       it_behaves_like :io_copy_stream_to_io, nil, IOSpecs::CopyStream
       it_behaves_like :io_copy_stream_to_io_with_offset, nil, IOSpecs::CopyStream
     end
+
+    describe "to a Tempfile" do
+      before :all do
+        require 'tempfile'
+      end
+
+      before :each do
+        @to_io = Tempfile.new("rubyspec_copy_stream", encoding: Encoding::BINARY, mode: File::RDONLY)
+        @to_name = @to_io.path
+      end
+
+      after :each do
+        @to_io.close!
+        @to_name = nil # do not rm_r it, already done by Tempfile#close!
+      end
+
+      it_behaves_like :io_copy_stream_to_io, nil, IOSpecs::CopyStream
+      it_behaves_like :io_copy_stream_to_io_with_offset, nil, IOSpecs::CopyStream
+    end
   end
 
   describe "from a file name" do
@@ -277,10 +300,8 @@
       @io.should_not_receive(:pos)
       IO.copy_stream(@io, @to_name)
     end
-
   end
 
-
   describe "with a destination that does partial reads" do
     before do
       @from_out, @from_in = IO.pipe