added test for copy_to; also, fixed it (rewind before copy)

lib/httpx/response.rb

@@ -150,6 +150,8 @@ module HTTPX
       def copy_to(dest)
         return unless @buffer
 
+        rewind
+
         if dest.respond_to?(:path) && @buffer.respond_to?(:path)
           FileUtils.mv(@buffer.path, dest.path)
         else

test/response_test.rb

@@ -49,6 +49,29 @@ class ResponseTest < Minitest::Test
     assert body3 == "", "HEAD requets body must be empty"
   end
 
+  def test_response_body_copy_to_memory
+    payload = "a" * 512
+    body = Response::Body.new(Response.new(request, 200, "2.0", {}), threshold_size: 1024)
+    body.write(payload)
+
+    memory = StringIO.new
+    body.copy_to(memory)
+    assert memory.string == payload, "didn't copy all bytes (expected #{payload.bytesize}, was #{memory.size})"
+    body.close
+  end
+
+  def test_response_body_copy_to_file
+    payload = "a" * 2048
+    body = Response::Body.new(Response.new(request, 200, "2.0", {}), threshold_size: 1024)
+    body.write(payload)
+
+    file = Tempfile.new("httpx-file-buffer")
+    body.copy_to(file)
+    assert File.read(file.path) == payload, "didn't copy all bytes (expected #{payload.bytesize}, was #{File.size(file.path)})"
+    body.close
+    file.unlink
+  end
+
   def test_response_body_read
     body1 = Response::Body.new(Response.new(request, 200, "2.0", {}), threshold_size: 1024)
     body1.write("foo")