There are some straggler rails version-specific tests/code that are not currently running. Some may have been accidentally omitted from running on newer rails versions; others may have been logic specific to those rails versions that were not actually needed/wanted on newer versions.

• Dead code? (folder doesn't exist I think, but test is passing anyway with and without rails)
  

  jruby-rack/src/spec/ruby/jruby/rack/booter_spec.rb

  Line 321 in bbbad30

  when '/WEB-INF' then File.expand_path('rails30/WEB-INF', STUB_DIR)

• Body closing
  

  jruby-rack/src/spec/ruby/jruby/rack/response_spec.rb

  Lines 389 to 396 in 6f88954

  	it "closes original body during write_body", :lib => [:rails30, :rails31, :rails32] do
  	body = wrap_file_body File.expand_path('../../files/image.jpg', File.dirname(__FILE__))
  	response = JRuby::Rack::Response.new [200, body.headers, body]
  	expect(body).to receive(:close)
  	response.write_body(response_environment)
  	end

• Dechunking?
  • may or may not be used/needed now (need to investigate whether JRuby::Rack::Response.dechunk = false is used/needed still).
    

    jruby-rack/src/spec/ruby/jruby/rack/response_spec.rb

    Lines 156 to 239 in 6f88954

    	it "dechunks the body when a chunked response is detected",
    	:lib => [:rails23, :rails31, :rails32, :rails40] do
    	require 'rack/chunked'
    	headers = {
    	"Cache-Control" => 'no-cache',
    	"Transfer-Encoding" => 'chunked'
    	}
    	body = [
    	"1".freeze,
    	"\nsecond chunk",
    	"a multi\nline chunk \n42",
    	"utf-8 chunk 'ty píčo'!\n",
    	"terminated chunk\r\n",
    	"", # should be skipped
    	"\r\nthe very\r\n last\r\n\r\n chunk"
    	]
    	with_dechunk do
    	body = Rack::Chunked::Body.new body
    	response = JRuby::Rack::Response.new([200, headers, body])
    	response.write_headers(response_environment)
    	times = 0
    	expect(stream).to receive(:write).exactly(6).times do |bytes|
    	str = String.from_java_bytes(bytes)
    	str = str.force_encoding('UTF-8') if str.respond_to?(:force_encoding)
    	case times += 1
    	when 1 then expect(str).to eq "1"
    	when 2 then expect(str).to eq "\nsecond chunk"
    	when 3 then expect(str).to eq "a multi\nline chunk \n42"
    	when 4 then expect(str).to eq "utf-8 chunk 'ty píčo'!\n"
    	when 5 then expect(str).to eq "terminated chunk\r\n"
    	when 6 then expect(str).to eq "\r\nthe very\r\n last\r\n\r\n chunk"
    	else
    	fail("unexpected :write received with #{str.inspect}")
    	end
    	end
    	expect(stream).to receive(:flush).exactly(6 + 1).times # +1 for tail chunk
    	response.write_body(response_environment)
    	end
    	end
    	it "does not dechunk body when dechunkins is turned off",
    	:lib => [:rails31, :rails32, :rails40] do
    	dechunk = JRuby::Rack::Response.dechunk?
    	begin
    	JRuby::Rack::Response.dechunk = false
    	require 'rack/chunked'
    	headers = {
    	"Cache-Control" => 'no-cache',
    	"Transfer-Encoding" => 'chunked'
    	}
    	body = [
    	"1".freeze,
    	"\nsecond chunk",
    	""
    	]
    	body = Rack::Chunked::Body.new body
    	response = JRuby::Rack::Response.new([200, headers, body])
    	response.write_headers(response_environment)
    	times = 0
    	expect(stream).to receive(:write).exactly(3).times do |bytes|
    	str = String.from_java_bytes(bytes)
    	case times += 1
    	when 1 then expect(str).to eq "1\r\n1\r\n"
    	when 2 then expect(str).to eq "d\r\n\nsecond chunk\r\n"
    	when 3 then expect(str).to eq "0\r\n\r\n"
    	else
    	fail("unexpected :write received with #{str.inspect}")
    	end
    	end
    	expect(stream).to receive(:flush).exactly(3).times
    	response.write_body(response_environment)
    	ensure
    	JRuby::Rack::Response.dechunk = dechunk
    	end
    	end

• Streaming files
  

  jruby-rack/src/spec/ruby/jruby/rack/response_spec.rb

  Lines 377 to 387 in 6f88954

  	it "streams a file using a channel if wrapped in body_parts",
  	:lib => [:rails30, :rails31, :rails32] do
  	body = wrap_file_body path =
  	File.expand_path('../../files/image.jpg', File.dirname(__FILE__))
  	stream = self.stream
  	response = JRuby::Rack::Response.new [200, body.headers, body]
  	response.write_body(response_environment)
  	expect_eql_java_bytes stream.to_java_bytes, File.read(path).to_java_bytes
  	end

Would also be good to review and remove the associated code if they were specific to ancient rails versions.