diff --git a/.circleci/config.yml b/.circleci/config.yml
new file mode 100644
index 0000000..38fd6a7
--- /dev/null
+++ b/.circleci/config.yml
@@ -0,0 +1,19 @@
+version: 2.1
+
+orbs:
+  ruby-orbs: sue445/ruby-orbs@volatile
+
+jobs:
+  test:
+    docker:
+      - image: cimg/ruby:3.0
+    steps:
+      - checkout
+      - ruby-orbs/bundle-install:
+          gemspec_name: fluent-plugin-time-series-counter
+          with_gemfile_lock: false
+      - run: bundle exec rake test
+workflows:
+  test:
+    jobs:
+      - test
diff --git a/Rakefile b/Rakefile
index 809eb56..97055e7 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,2 +1,11 @@
 require "bundler/gem_tasks"
+require 'rake/testtask'
 
+Rake::Task[:release].clear
+
+Rake::TestTask.new(:test) do |t|
+  t.libs << 'lib' << 'test'
+  t.pattern = 'test/**/test_*.rb'
+end
+
+task default: :test
diff --git a/fluent-plugin-time-series-counter.gemspec b/fluent-plugin-time-series-counter.gemspec
index 342d85b..76b975d 100644
--- a/fluent-plugin-time-series-counter.gemspec
+++ b/fluent-plugin-time-series-counter.gemspec
@@ -16,6 +16,8 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
-  spec.add_development_dependency "bundler", "~> 1.7"
-  spec.add_development_dependency "rake", "~> 10.0"
+  spec.add_dependency 'fluentd', '>= 1', '< 2'
+
+  spec.add_development_dependency 'rake'
+  spec.add_development_dependency 'test-unit'
 end
diff --git a/lib/fluent/plugin/out_time_series_counter.rb b/lib/fluent/plugin/out_time_series_counter.rb
index 62daae1..6193978 100644
--- a/lib/fluent/plugin/out_time_series_counter.rb
+++ b/lib/fluent/plugin/out_time_series_counter.rb
@@ -1,113 +1,102 @@
-module Fluent
-  class TimeSeriesCounter < Fluent::BufferedOutput
-    Fluent::Plugin.register_output('time_series_counter', self)
-
-    unless method_defined?(:log)
-      define_method('log') { $log }
+require 'fluent/plugin/output'
+
+class Fluent::Plugin::TimeSeriesCounter < Fluent::Plugin::Output
+  Fluent::Plugin.register_output('time_series_counter', self)
+  helpers :event_emitter
+
+  config_param :tag, :string, default: "tsc"
+  config_param :count_keys, :array, value_type: :string, alias: :count_key
+  config_param :count_key_delimiter, :string, default: ":"
+  config_param :count_value_name, :string, default: "count"
+  config_param :unit, :array, value_type: :string
+  config_param :uniq_key, :string, default: "tsc_key"
+  config_param :unit_key, :string, default: "tsc_unit"
+  config_param :time_key, :string, default: "tsc_time"
+
+  def configure(conf)
+    super
+
+    @units = unit.inject({}) do |hash, i|
+      hash[i] = true
+      hash
     end
+  end
 
-    config_param :tag, :string, :default => "tsc"
-    config_param :count_key, :string, :default => nil
-    config_param :count_key_delimiter, :string, :default => ":"
-    config_param :count_value_name, :string, :default => "count"
-    config_param :unit, :string, :default => nil
-    config_param :uniq_key, :string, :default => "tsc_key"
-    config_param :unit_key, :string, :default => "tsc_unit"
-    config_param :time_key, :string, :default => "tsc_time"
-
-    def initialize
-      super
-    end
+  def formatted_to_msgpack_binary?
+    true
+  end
 
-    def configure(conf)
-      super
 
-      if !count_key
-        raise ConfigError, "out_time_series_counter: required 'count_key' parameter."
-      end
+  def format(tag, time, record)
+    [tag, time, record].to_msgpack
+  end
 
-      if !unit
-        raise ConfigError, "out_time_series_counter: required 'unit' parameter."
+  def write(chunk)
+    stats = {}
+
+    chunk.msgpack_each do |tag, time, record|
+      skip = false
+
+      @count_keys.each do |k|
+        # skip record if a record does not have requried count_keys
+        skip = true unless record[k]
       end
+      next if skip
 
-      @count_keys = count_key.split(/\s*,\s*/).sort
-      @unit = unit.split(/\s*,\s*/).inject({}) do |hash, i|
-        hash[i] = true
-        hash
+      if @units['min']
+        count(stats, record, time, "min")
       end
-    end
 
-    def format(tag, time, record)
-      [tag, time, record].to_msgpack
-    end
+      if @units['hour']
+        count(stats, record, time, "hour")
+      end
 
-    def write(chunk)
-      stats = {}
-      chunk.msgpack_each do |tag, time, record|
-        skip = false
-        next unless time
-        @count_keys.each do |k|
-          # skip record if a record does not have requried count_keys
-          skip = true unless record[k]
-        end
-        next if skip
-
-        if @unit['min']
-          count(stats, record, time, "min")
-        end
-
-        if @unit['hour']
-          count(stats, record, time, "hour")
-        end
-
-        if @unit['day']
-          count(stats, record, time, "day")
-        end
+      if @units['day']
+        count(stats, record, time, "day")
       end
+    end
+    output_stats(stats)
+  end
 
-      output_stats(stats)
+  private
+  def create_uniq_key(record, unit, time)
+    uniq_key = []
+    @count_keys.each do |k|
+      uniq_key << record[k]
     end
+    uniq_key << time.to_s
+    uniq_key << unit
+    uniq_key.join(@count_key_delimiter)
+  end
 
-    private
-    def create_uniq_key(record, unit, time)
-      uniq_key = []
-      @count_keys.each do |k|
-        uniq_key << record[k]
-      end
-      uniq_key << time.to_s
-      uniq_key << unit
-      uniq_key.join(@count_key_delimiter)
+  def count(stats, record, time, unit)
+    case unit
+    when "min"
+      unit_time = time - (time % 60)
+    when "hour"
+      unit_time = time - (time % 3600)
+    when "day"
+      unit_time = time - (time % 86400)
+    else
+      return
     end
 
-    def count(stats, record, time, unit)
-      unix_time = 0
-      case unit
-      when "min"
-        unit_time = time - (time % 60)
-      when "hour"
-        unit_time = time - (time % 3600)
-      when "day"
-        unit_time = time - (time % 86400)
-      else
-        return
-      end
-      tsc_key = create_uniq_key(record, unit, unit_time)
-      unless stats[tsc_key]
-        stats[tsc_key] = {@count_value_name => 0} unless stats[tsc_key]
-        @count_keys.each do |k|
-          stats[tsc_key][k] = record[k]
-        end
-        stats[tsc_key][@unit_key] = unit
-        stats[tsc_key][@time_key] = unit_time
+    tsc_key = create_uniq_key(record, unit, unit_time)
+    unless stats[tsc_key]
+      stats[tsc_key] = {@count_value_name => 0} unless stats[tsc_key]
+      @count_keys.each do |k|
+        stats[tsc_key][k] = record[k]
       end
-      stats[tsc_key][@count_value_name] += 1
+      stats[tsc_key][@unit_key] = unit
+      stats[tsc_key][@time_key] = unit_time
     end
+    stats[tsc_key][@count_value_name] += 1
+  end
 
-    def output_stats(stats)
-      stats.each do |k, v|
-        v[@uniq_key] = k
-        Fluent::Engine.emit("#{@tag}", Fluent::Engine.now, v)
-      end
+  def output_stats(stats)
+    stats.each do |k, v|
+      v[@uniq_key] = k
+      router.emit(@tag, Fluent::Engine.now, v)
     end
   end
 end
diff --git a/test/helper.rb b/test/helper.rb
new file mode 100644
index 0000000..f9e989a
--- /dev/null
+++ b/test/helper.rb
@@ -0,0 +1,8 @@
+$LOAD_PATH.unshift(File.expand_path("../../", __FILE__))
+require "test-unit"
+require "fluent/test"
+require "fluent/test/driver/output"
+require "fluent/test/helpers"
+
+Test::Unit::TestCase.include(Fluent::Test::Helpers)
+Test::Unit::TestCase.extend(Fluent::Test::Helpers)
diff --git a/test/plugin/test_out_time_series_counter.rb b/test/plugin/test_out_time_series_counter.rb
new file mode 100644
index 0000000..8f59644
--- /dev/null
+++ b/test/plugin/test_out_time_series_counter.rb
@@ -0,0 +1,151 @@
+require 'helper'
+
+require 'fluent/plugin/out_time_series_counter'
+
+class TimeSeriesCounterTest < Test::Unit::TestCase
+  include Fluent::Test::Helpers
+
+  def setup
+    Fluent::Test.setup   # Setup test for Fluentd (Required)
+  end
+
+  CONFIG = %[
+    count_key id
+    unit hour
+  ]
+
+  def create_driver(conf = CONFIG)
+    Fluent::Test::Driver::Output.new(Fluent::Plugin::TimeSeriesCounter).configure(conf)
+  end
+
+  sub_test_case 'configuration' do
+    test 'basic configuration' do
+      d = create_driver
+      assert_equal ['id'], d.instance.count_keys
+      assert_equal ['hour'], d.instance.unit
+    end
+
+    test 'invalid configration' do
+      assert_raise(Fluent::ConfigError) {
+        create_driver(
+          <<~EOS
+            count_key id
+          EOS
+        )
+      }
+
+      assert_raise(Fluent::ConfigError) {
+        create_driver(
+          <<~EOS
+            unit hour
+          EOS
+        )
+      }
+    end
+  end
+
+  sub_test_case 'count' do
+    test 'count per count_key' do
+      d = create_driver
+      d.run(default_tag: 'test') do
+        d.feed({'id' => 1})
+        d.feed({'id' => 1})
+        d.feed({'id' => 2})
+      end
+
+      # result == uniq(count_key)
+      assert_equal(2, d.events.size)
+
+      results = d.events.flat_map{|_key, _time, result| result }
+
+      result = results.find{ |r| r["id"] == 1 }
+      assert_equal(2, result["count"])
+
+      result = results.find{ |r| r["id"] == 2 }
+      assert_equal(1, result["count"])
+    end
+
+    test 'count per unit(hour)' do
+      d = create_driver
+
+      d.run(default_tag: 'test') do
+        d.feed(event_time('2022-09-01 10:00:00 UTC'), {'id' => 1})
+        d.feed(event_time('2022-09-01 10:00:00 UTC'), {'id' => 1})
+
+        d.feed(event_time('2022-09-01 11:00:00 UTC'), {'id' => 1})
+      end
+
+      # result == uniq(count_key)
+      assert_equal(2, d.events.size)
+
+      results = d.events.flat_map{|_key, _time, result| result }
+
+      # Time.at(1662026400) => 2022-09-01 10:00:00 UTC
+      result = results.find{ |r| r["tsc_time"] == 1662026400 }
+      assert_equal(2, result["count"])
+
+      # Time.at(1662030000) => 2022-09-01 11:00:00 UTC
+      result = results.find{ |r| r["tsc_time"] == 1662030000 }
+      assert_equal(1, result["count"])
+    end
+
+    test 'count only feeds with all keys' do
+      d = create_driver(
+        <<~EOS
+          count_key a,b,c
+          unit hour
+        EOS
+      )
+
+      d.run(default_tag: 'test') do
+        # no count
+        d.feed({a: 1})
+        d.feed({a: 1, b: 2})
+        d.feed({a: 1, b: 2})
+
+        # count
+        d.feed({a: 1, b: 2, c: 3})
+        d.feed({a: 1, b: 2, c: 3})
+        d.feed({a: 1, b: 2, c: 3})
+      end
+
+      assert_equal(1, d.events.size)
+
+      _key, _time, record = d.events.first
+
+      assert_equal(3, record['count'])
+    end
+
+    test 'count per units' do
+      d = create_driver(
+        <<~EOS
+          count_key id
+          unit min,hour,day
+        EOS
+      )
+
+      d.run(default_tag: 'test') do
+        d.feed(event_time('2022-09-01 10:00:00 UTC'), {'id' => 1})
+        d.feed(event_time('2022-09-01 10:01:00 UTC'), {'id' => 1})
+
+        d.feed(event_time('2022-09-01 11:00:00 UTC'), {'id' => 1})
+
+        d.feed(event_time('2022-09-02 10:00:00 UTC'), {'id' => 1})
+        d.feed(event_time('2022-09-02 10:00:00 UTC'), {'id' => 1})
+        d.feed(event_time('2022-09-02 10:00:00 UTC'), {'id' => 1})
+
+        d.feed(event_time('2022-09-01 10:00:00 UTC'), {'id' => 2})
+      end
+
+      results = d.events.map{|_,_,r| r}
+
+      assert_equal(4, results.count{|r| r['id'] == 1 && r['tsc_unit'] == 'min'})
+      assert_equal(3, results.count{|r| r['id'] == 1 && r['tsc_unit'] == 'hour'})
+      assert_equal(2, results.count{|r| r['id'] == 1 && r['tsc_unit'] == 'day'})
+
+      assert_equal(1, results.count{|r| r['id'] == 2 && r['tsc_unit'] == 'min'})
+      assert_equal(1, results.count{|r| r['id'] == 2 && r['tsc_unit'] == 'hour'})
+      assert_equal(1, results.count{|r| r['id'] == 2 && r['tsc_unit'] == 'day'})
+    end
+  end
+end