added plugin tests, and the plugin body

lib/httpx/plugins/response_cache.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+module HTTPX
+  module Plugins
+    #
+    # This plugin adds support for retrying requests when certain errors happen.
+    #
+    # https://gitlab.com/honeyryderchuck/httpx/wikis/Response-Cache
+    #
+    module ResponseCache
+    end
+    register_plugin :response_cache, ResponseCache
+  end
+end

test/http_test.rb

@@ -30,6 +30,7 @@ class HTTPTest < Minitest::Test
   include Plugins::AWSAuthentication
   include Plugins::Upgrade
   include Plugins::GRPC if RUBY_ENGINE == "ruby" && RUBY_VERSION >= "2.3.0"
+  include Plugins::ResponseCache
 
   def test_verbose_log
     log = StringIO.new

test/https_test.rb

@@ -31,6 +31,7 @@ class HTTPSTest < Minitest::Test
   include Plugins::AWSAuthentication
   include Plugins::Upgrade
   include Plugins::GRPC if RUBY_ENGINE == "ruby" && RUBY_VERSION >= "2.3.0"
+  include Plugins::ResponseCache
 
   def test_connection_coalescing
     coalesced_origin = "https://#{ENV["HTTPBIN_COALESCING_HOST"]}"

test/support/requests/plugins/response_cache.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require "securerandom"
+
+module Requests
+  module Plugins
+    module ResponseCache
+      def test_plugin_response_cache_etag
+        cache_client = HTTPX.plugin(:response_cache)
+        etag = SecureRandom.hex
+
+        etag_uri = build_uri("/cache")
+
+        uncached = cache_client.get(etag_uri)
+        verify_status(uncached, 200)
+        cached = cache_client.get(etag_uri)
+        verify_status(cached, 304)
+
+        assert uncached.body == cached.body
+
+        cached.clear_response_cache
+
+        uncached = cache_client.get(etag_uri)
+        verify_status(uncached, 200)
+      end
+
+      def test_plugin_response_cache_cache_control
+        cache_client = HTTPX.plugin(:response_cache)
+        cache_control = 2
+
+        cache_control_uri = build_uri("/cache/#{cache_control}")
+
+        uncached = cache_client.get(cache_control_uri)
+        verify_status(uncached, 200)
+        cached = cache_client.get(cache_control_uri)
+        verify_status(cached, 304)
+
+        assert uncached == cached
+        sleep(2)
+        expired = cache_client.get(cache_control_uri)
+        verify_status(expired, 200)
+
+        assert expired != uncached
+      end
+    end
+  end
+end