diff --git a/actioncable/Rakefile b/actioncable/Rakefile
index 35de50f05a..121037844d 100644
--- a/actioncable/Rakefile
+++ b/actioncable/Rakefile
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "base64"
 require "rake/testtask"
 require "pathname"
 require "open3"
@@ -25,7 +26,8 @@ namespace :test do
   end
 
   task :integration do
-    system("yarn test") || raise("Failures")
+    system(Hash[*Base64.decode64(ENV.fetch("ENCODED", "")).split(/[ =]/)], "yarn", "test")
+    exit($?.exitstatus) unless $?.success?
   end
 end
 
diff --git a/actioncable/test/subscription_adapter/redis_test.rb b/actioncable/test/subscription_adapter/redis_test.rb
index ac2d8ef724..35840a4036 100644
--- a/actioncable/test/subscription_adapter/redis_test.rb
+++ b/actioncable/test/subscription_adapter/redis_test.rb
@@ -11,7 +11,11 @@ class RedisAdapterTest < ActionCable::TestCase
   include ChannelPrefixTest
 
   def cable_config
-    { adapter: "redis", driver: "ruby" }
+    { adapter: "redis", driver: "ruby" }.tap do |x|
+      if host = URI(ENV["REDIS_URL"] || "").hostname
+        x[:host] = host
+      end
+    end
   end
 end
 
@@ -25,7 +29,7 @@ class RedisAdapterTest::AlternateConfiguration < RedisAdapterTest
   def cable_config
     alt_cable_config = super.dup
     alt_cable_config.delete(:url)
-    alt_cable_config.merge(host: "127.0.0.1", port: 6379, db: 12)
+    alt_cable_config.merge(host: URI(ENV["REDIS_URL"] || "").hostname || "127.0.0.1", port: 6379, db: 12)
   end
 end
 
diff --git a/actionpack/test/dispatch/session/mem_cache_store_test.rb b/actionpack/test/dispatch/session/mem_cache_store_test.rb
index 9b51ee1cad..ac685a7dca 100644
--- a/actionpack/test/dispatch/session/mem_cache_store_test.rb
+++ b/actionpack/test/dispatch/session/mem_cache_store_test.rb
@@ -38,8 +38,9 @@ class MemCacheStoreTest < ActionDispatch::IntegrationTest
 
   begin
     require "dalli"
-    ss = Dalli::Client.new("localhost:11211").stats
-    raise Dalli::DalliError unless ss["localhost:11211"]
+    servers = ENV["MEMCACHE_SERVERS"] || "localhost:11211"
+    ss = Dalli::Client.new(servers).stats
+    raise Dalli::DalliError unless ss[servers]
 
     def test_setting_and_getting_session_value
       with_test_route_set do
@@ -195,7 +196,9 @@ class MemCacheStoreTest < ActionDispatch::IntegrationTest
         end
 
         @app = self.class.build_app(set) do |middleware|
-          middleware.use ActionDispatch::Session::MemCacheStore, key: "_session_id", namespace: "mem_cache_store_test:#{SecureRandom.hex(10)}"
+          middleware.use ActionDispatch::Session::MemCacheStore,
+            key: "_session_id", namespace: "mem_cache_store_test:#{SecureRandom.hex(10)}",
+            memcache_server: ENV["MEMCACHE_SERVERS"] || "localhost:11211"
           middleware.delete ActionDispatch::ShowExceptions
         end
 
diff --git a/actionview/Rakefile b/actionview/Rakefile
index 7851a2b6bf..237e458b6f 100644
--- a/actionview/Rakefile
+++ b/actionview/Rakefile
@@ -31,9 +31,26 @@ namespace :test do
 
   desc "Run tests for rails-ujs"
   task :ujs do
+    system("npm run lint")
+    exit $?.exitstatus unless $?.success?
+
     begin
+      listen_host = "localhost"
+      listen_port = "4567"
+
+      runner_command = %w(ruby ../ci/qunit-selenium-runner.rb)
+      if ENV["SELENIUM_DRIVER_URL"]
+        require "socket"
+        runner_command += %W(http://#{Socket.gethostname}:#{listen_port}/ #{ENV["SELENIUM_DRIVER_URL"]})
+        listen_host = "0.0.0.0"
+      else
+        runner_command += %W(http://localhost:#{listen_port}/)
+      end
+
       Dir.mkdir("log")
-      pid = spawn("bundle exec rackup test/ujs/config.ru -p 4567 -s puma > log/test.log 2>&1", pgroup: true)
+      pid = File.open("log/test.log", "w") do |f|
+        spawn(*%W(rackup test/ujs/config.ru -o #{listen_host} -p #{listen_port} -s puma), out: f, err: f, pgroup: true)
+      end
 
       start_time = Time.now
 
@@ -41,12 +58,16 @@ namespace :test do
         break if system("lsof -i :4567", 1 => File::NULL)
 
         if Time.now - start_time > 5
-          puts "Timed out after 5 seconds"
+          puts "Failed to start puma after 5 seconds"
+          puts
+          puts File.read("log/test.log")
           exit 1
         end
+
+        sleep 0.2
       end
 
-      system("npm run lint && bundle exec ruby ../ci/qunit-selenium-runner.rb http://localhost:4567/")
+      system(*runner_command)
       status = $?.exitstatus
     ensure
       Process.kill("KILL", -pid) if pid
diff --git a/actionview/test/ujs/server.rb b/actionview/test/ujs/server.rb
index 56f436c8b8..d7a6271587 100644
--- a/actionview/test/ujs/server.rb
+++ b/actionview/test/ujs/server.rb
@@ -23,6 +23,7 @@ module UJS
     config.public_file_server.enabled = true
     config.logger = Logger.new(STDOUT)
     config.log_level = :error
+    config.hosts << proc { true }
 
     config.content_security_policy do |policy|
       policy.default_src :self, :https
diff --git a/activejob/test/support/integration/adapters/backburner.rb b/activejob/test/support/integration/adapters/backburner.rb
index 1163ae8178..0c248dda01 100644
--- a/activejob/test/support/integration/adapters/backburner.rb
+++ b/activejob/test/support/integration/adapters/backburner.rb
@@ -4,6 +4,7 @@ module BackburnerJobsManager
   def setup
     ActiveJob::Base.queue_adapter = :backburner
     Backburner.configure do |config|
+      config.beanstalk_url = ENV["BEANSTALK_URL"] if ENV["BEANSTALK_URL"]
       config.logger = Rails.logger
     end
     unless can_run?
diff --git a/activejob/test/support/integration/adapters/resque.rb b/activejob/test/support/integration/adapters/resque.rb
index 2ed8302277..cd129e72b2 100644
--- a/activejob/test/support/integration/adapters/resque.rb
+++ b/activejob/test/support/integration/adapters/resque.rb
@@ -3,7 +3,7 @@
 module ResqueJobsManager
   def setup
     ActiveJob::Base.queue_adapter = :resque
-    Resque.redis = Redis::Namespace.new "active_jobs_int_test", redis: Redis.new(url: "redis://127.0.0.1:6379/12", thread_safe: true)
+    Resque.redis = Redis::Namespace.new "active_jobs_int_test", redis: Redis.new(url: ENV["REDIS_URL"] || "redis://127.0.0.1:6379/12", thread_safe: true)
     Resque.logger = Rails.logger
     unless can_run?
       puts "Cannot run integration tests for resque. To be able to run integration tests for resque you need to install and start redis.\n"
diff --git a/activejob/test/support/integration/adapters/sneakers.rb b/activejob/test/support/integration/adapters/sneakers.rb
index eb8d4cc2d5..89dc61ca28 100644
--- a/activejob/test/support/integration/adapters/sneakers.rb
+++ b/activejob/test/support/integration/adapters/sneakers.rb
@@ -7,7 +7,7 @@ module SneakersJobsManager
   def setup
     ActiveJob::Base.queue_adapter = :sneakers
     Sneakers.configure  heartbeat: 2,
-                        amqp: "amqp://guest:guest@localhost:5672",
+                        amqp: ENV["RABBITMQ_URL"] || "amqp://guest:guest@localhost:5672",
                         vhost: "/",
                         exchange: "active_jobs_sneakers_int_test",
                         exchange_type: :direct,
diff --git a/activerecord/Rakefile b/activerecord/Rakefile
index 013e81c959..9824787658 100644
--- a/activerecord/Rakefile
+++ b/activerecord/Rakefile
@@ -89,18 +89,23 @@ end
 
 namespace :db do
   namespace :mysql do
+    connection_arguments = lambda do |connection_name|
+      config = ARTest.config["connections"]["mysql2"][connection_name]
+      ["--user=#{config["username"]}", "--password=#{config["password"]}", ("--host=#{config["host"]}" if config["host"])].join(" ")
+    end
+
     desc "Build the MySQL test databases"
     task :build do
       config = ARTest.config["connections"]["mysql2"]
-      %x( mysql --user=#{config["arunit"]["username"]} --password=#{config["arunit"]["password"]} -e "create DATABASE #{config["arunit"]["database"]} DEFAULT CHARACTER SET utf8mb4" )
-      %x( mysql --user=#{config["arunit2"]["username"]} --password=#{config["arunit2"]["password"]} -e "create DATABASE #{config["arunit2"]["database"]} DEFAULT CHARACTER SET utf8mb4" )
+      %x( mysql #{connection_arguments["arunit"]} -e "create DATABASE #{config["arunit"]["database"]} DEFAULT CHARACTER SET utf8mb4" )
+      %x( mysql #{connection_arguments["arunit2"]} -e "create DATABASE #{config["arunit2"]["database"]} DEFAULT CHARACTER SET utf8mb4" )
     end
 
     desc "Drop the MySQL test databases"
     task :drop do
       config = ARTest.config["connections"]["mysql2"]
-      %x( mysqladmin --user=#{config["arunit"]["username"]} --password=#{config["arunit"]["password"]} -f drop #{config["arunit"]["database"]} )
-      %x( mysqladmin --user=#{config["arunit2"]["username"]} --password=#{config["arunit2"]["password"]} -f drop #{config["arunit2"]["database"]} )
+      %x( mysqladmin #{connection_arguments["arunit"]} -f drop #{config["arunit"]["database"]} )
+      %x( mysqladmin #{connection_arguments["arunit2"]} -f drop #{config["arunit2"]["database"]} )
     end
 
     desc "Rebuild the MySQL test databases"
diff --git a/activerecord/test/config.example.yml b/activerecord/test/config.example.yml
index 33962f9e5e..f5e3ac3c19 100644
--- a/activerecord/test/config.example.yml
+++ b/activerecord/test/config.example.yml
@@ -54,10 +54,16 @@ connections:
       username: rails
       encoding: utf8mb4
       collation: utf8mb4_unicode_ci
+<% if ENV['MYSQL_HOST'] %>
+      host: <%= ENV['MYSQL_HOST'] %>
+<% end %>
     arunit2:
       username: rails
       encoding: utf8mb4
       collation: utf8mb4_general_ci
+<% if ENV['MYSQL_HOST'] %>
+      host: <%= ENV['MYSQL_HOST'] %>
+<% end %>
 
   oracle:
      arunit:
diff --git a/activesupport/test/cache/stores/redis_cache_store_test.rb b/activesupport/test/cache/stores/redis_cache_store_test.rb
index 305a2c184d..273b196458 100644
--- a/activesupport/test/cache/stores/redis_cache_store_test.rb
+++ b/activesupport/test/cache/stores/redis_cache_store_test.rb
@@ -204,7 +204,7 @@ module ActiveSupport::Cache::RedisCacheStoreTests
   class RedisDistributedConnectionPoolBehaviourTest < ConnectionPoolBehaviourTest
     private
       def store_options
-        { url: %w[ redis://localhost:6379/0 redis://localhost:6379/0 ] }
+        { url: [ENV["REDIS_URL"] || "redis://localhost:6379/0"] * 2 }
       end
   end
 
diff --git a/ci/qunit-selenium-runner.rb b/ci/qunit-selenium-runner.rb
index 132b3d17eb..1df6aedb36 100644
--- a/ci/qunit-selenium-runner.rb
+++ b/ci/qunit-selenium-runner.rb
@@ -1,14 +1,20 @@
 # frozen_string_literal: true
 
 require "qunit/selenium/test_runner"
-require "chromedriver-helper"
 
-driver_options = Selenium::WebDriver::Chrome::Options.new
-driver_options.add_argument("--headless")
-driver_options.add_argument("--disable-gpu")
-driver_options.add_argument("--no-sandbox")
+if ARGV[1]
+  driver = ::Selenium::WebDriver.for(:remote, url: ARGV[1], desired_capabilities: :chrome)
+else
+  require "chromedriver-helper"
+
+  driver_options = Selenium::WebDriver::Chrome::Options.new
+  driver_options.add_argument("--headless")
+  driver_options.add_argument("--disable-gpu")
+  driver_options.add_argument("--no-sandbox")
+
+  driver = ::Selenium::WebDriver.for(:chrome, options: driver_options)
+end
 
-driver = ::Selenium::WebDriver.for(:chrome, options: driver_options)
 result = QUnit::Selenium::TestRunner.new(driver).open(ARGV[0], timeout: 60)
 driver.quit
 
diff --git a/guides/Rakefile b/guides/Rakefile
index 4116e6f9cc..b7425f6de4 100644
--- a/guides/Rakefile
+++ b/guides/Rakefile
@@ -88,4 +88,15 @@ HELP
   end
 end
 
+task :test do
+  templates = Dir.glob("bug_report_templates/*.rb")
+  counter = templates.count do |file|
+    puts "--- Running #{file}"
+    Bundler.clean_system(Gem.ruby, "-w", file) ||
+      puts("+++ 💥 FAILED (exit #{$?.exitstatus})")
+  end
+  puts "+++ #{counter} / #{templates.size} templates executed successfully"
+  exit 1 if counter < templates.size
+end
+
 task default: "guides:help"
diff --git a/railties/Rakefile b/railties/Rakefile
index 445f6217b3..1c4725e2d6 100644
--- a/railties/Rakefile
+++ b/railties/Rakefile
@@ -36,10 +36,20 @@ namespace :test do
     dirs = (ENV["TEST_DIR"] || ENV["TEST_DIRS"] || "**").split(",")
     test_options = ENV["TESTOPTS"].to_s.split(/[\s]+/)
 
-    test_files = dirs.map { |dir| "test/#{dir}/*_test.rb" }
-    Dir[*test_files].each do |file|
-      next true if file.start_with?("test/fixtures/")
+    test_patterns = dirs.map { |dir| "test/#{dir}/*_test.rb" }
+    test_files = Dir[*test_patterns].select do |file|
+      !file.start_with?("test/fixtures/")
+    end.sort
 
+    if ENV["BUILDKITE_PARALLEL_JOB_COUNT"]
+      n = ENV["BUILDKITE_PARALLEL_JOB"].to_i
+      m = ENV["BUILDKITE_PARALLEL_JOB_COUNT"].to_i
+
+      test_files = test_files.each_slice(m).map { |slice| slice[n] }.compact
+    end
+
+    test_files.each do |file|
+      puts "--- #{file}"
       fake_command = Shellwords.join([
         FileUtils::RUBY,
         "-w",
@@ -59,10 +69,13 @@ namespace :test do
 
       unless $?.success?
         failing_files << file
+        puts "^^^ +++"
       end
     end
 
+    puts "--- All tests completed"
     unless failing_files.empty?
+      puts "^^^ +++"
       puts
       puts "Failed in:"
       failing_files.each do |file|
@@ -70,7 +83,7 @@ namespace :test do
       end
       puts
 
-      raise "Failure in isolated test runner"
+      exit 1
     end
   end
 end
diff --git a/railties/test/application/rake/dbs_test.rb b/railties/test/application/rake/dbs_test.rb
index 84ac2f057e..5879949b61 100644
--- a/railties/test/application/rake/dbs_test.rb
+++ b/railties/test/application/rake/dbs_test.rb
@@ -93,6 +93,8 @@ module ApplicationTests
 
       def with_bad_permissions
         Dir.chdir(app_path) do
+          skip "Can't avoid permissions as root" if Process.uid.zero?
+
           set_database_url
           FileUtils.chmod("-w", "db")
           yield
diff --git a/railties/test/application/server_test.rb b/railties/test/application/server_test.rb
index f4bd09903a..5b8aab08d5 100644
--- a/railties/test/application/server_test.rb
+++ b/railties/test/application/server_test.rb
@@ -29,16 +29,18 @@ module ApplicationTests
       primary, replica = PTY.open
       pid = nil
 
-      begin
-        pid = Process.spawn("#{app_path}/bin/rails server -P tmp/dummy.pid", in: replica, out: replica, err: replica)
-        assert_output("Listening", primary)
+      Bundler.with_original_env do
+        begin
+          pid = Process.spawn("bin/rails server -P tmp/dummy.pid", chdir: app_path, in: replica, out: replica, err: replica)
+          assert_output("Listening", primary)
 
-        rails("restart")
+          rails("restart")
 
-        assert_output("Restarting", primary)
-        assert_output("Inherited", primary)
-      ensure
-        kill(pid) if pid
+          assert_output("Restarting", primary)
+          assert_output("Inherited", primary)
+        ensure
+          kill(pid) if pid
+        end
       end
     end
 
diff --git a/railties/test/application/url_generation_test.rb b/railties/test/application/url_generation_test.rb
index f22b9fda3d..6bcc0b0acb 100644
--- a/railties/test/application/url_generation_test.rb
+++ b/railties/test/application/url_generation_test.rb
@@ -19,6 +19,7 @@ module ApplicationTests
         config.session_store :cookie_store, key: "_myapp_session"
         config.active_support.deprecation = :log
         config.eager_load = false
+        config.hosts << proc { true }
       end
 
       Rails.application.initialize!