diff --git a/.circleci/config.yml b/.circleci/config.yml
new file mode 100644
index 00000000..c76072a8
--- /dev/null
+++ b/.circleci/config.yml
@@ -0,0 +1,12 @@
+jobs:
+  build:
+    docker:
+      - image: cimg/ruby:3.3.5
+    environment:
+      RAILS_ENV: test
+    steps:
+      - checkout
+      - run: |
+          bundle install
+      - run: |
+          bundle exec rake test
diff --git a/.travis.yml b/.travis.yml
index a8f407e5..6c607d27 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,6 +3,7 @@ env:
     - "JRUBY_OPTS=-Xcext.enabled=true"
     - "CC_TEST_REPORTER_ID=faa393209ff0a104cf37511a9a03510bcee37951971b1ca4ffc2af217851d47e"
 language: ruby
+os: linux
 rvm:
   - 1.8.7
   - ree
@@ -15,11 +16,15 @@ rvm:
   - 2.5
   - 2.6
   - 2.7
+  - 3.0
+  - 3.1
+  - 3.2
   - ruby-head
   - jruby
-matrix:
+jobs:
   allow_failures:
     - rvm: 1.8.7
+    - rvm: ree
     - rvm: ruby-head
     - rvm: jruby
 branches:
@@ -33,4 +38,3 @@ before_script:
 script: "rake test" # test:scanners"
 after_script:
   - ./cc-test-reporter after-build --exit-code $TRAVIS_TEST_RESULT
-sudo: false
diff --git a/README.markdown b/README.markdown
index 410d1bff..a768ef10 100644
--- a/README.markdown
+++ b/README.markdown
@@ -1,7 +1,6 @@
 # CodeRay
 
-[![Build Status](https://travis-ci.org/rubychan/coderay.svg?branch=master)](https://travis-ci.org/rubychan/coderay)
-[![Gem Version](https://badge.fury.io/rb/coderay.svg)](https://badge.fury.io/rb/coderay) [![Maintainability](https://api.codeclimate.com/v1/badges/e015bbd5eab45d948b6b/maintainability)](https://codeclimate.com/github/rubychan/coderay/maintainability)
+[![CircleCI](https://dl.circleci.com/status-badge/img/gh/rubychan/coderay/tree/master.svg?style=svg&circle-token=CCIPRJ_BbFff6nMhNtPdrCBNMDxNq_be00bbb00849a29d8d8d2e28e7b84cbf76a9ee5c)](https://dl.circleci.com/status-badge/redirect/gh/rubychan/coderay/tree/master) [![Gem Version](https://badge.fury.io/rb/coderay.svg)](https://badge.fury.io/rb/coderay) [![Maintainability](https://api.codeclimate.com/v1/badges/e015bbd5eab45d948b6b/maintainability)](https://codeclimate.com/github/rubychan/coderay/maintainability)
 
 ## About
 
diff --git a/test/unit/debug.rb b/test/unit/debug.rb
index 88baf563..b694f21e 100644
--- a/test/unit/debug.rb
+++ b/test/unit/debug.rb
@@ -24,7 +24,8 @@ def test_creation
     ["   \n", :space],
     ["[]", :method],
     [:end_line, :head],
-  ].flatten
+  ]
+  TEST_INPUT.flatten!
   TEST_OUTPUT = <<-'DEBUG'.chomp
 integer(10)operator((\\\))string<content(test)>head[
 
diff --git a/test/unit/statistic.rb b/test/unit/statistic.rb
index 1326dca6..776774d4 100644
--- a/test/unit/statistic.rb
+++ b/test/unit/statistic.rb
@@ -24,7 +24,8 @@ def test_creation
     ["   \n", :space],
     ["[]", :method],
     [:end_line, :test],
-  ].flatten
+  ]
+  TEST_INPUT.flatten!
   TEST_OUTPUT = <<-'DEBUG'
 
 Code Statistics
@@ -56,4 +57,4 @@ def test_filtering_text_tokens
     assert_equal TEST_OUTPUT, TEST_INPUT.statistic
   end
   
-end
\ No newline at end of file
+end