Test with help of CircleCI

CircleCI provides much faster builds than TravisCI:

CircleCI - less than 1 minute
TravisCI- 6 minutes

The cost is the complexity of the config:
https://circleci.com/docs/2.0/configuration-reference/

.circleci/config.yml

@@ -0,0 +1,159 @@
+version: 2
+references:
+  repo_restore_cache: &repo_restore_cache
+    restore_cache:
+      keys:
+        - repo-{{ .Environment.CIRCLE_SHA1 }}
+
+  repo_save_cache: &repo_save_cache
+    save_cache:
+      key: repo-{{ .Environment.CIRCLE_SHA1 }}-{{ epoch }}
+      paths:
+        - ~/pry
+
+  bundle_install: &bundle_install
+    run:
+      name: Install Bundler dependencies
+      command: bundle install --path ~/pry/vendor/bundle --jobs 15
+
+  unit: &unit
+    run:
+      name: Run unit tests
+      command: bundle exec rake
+
+  install_alpine_nano: &install_alpine_nano
+    run:
+      name: Install Nano text editor on Alpine Linux
+      command: apk add nano
+
+  install_ubuntu_nano: &install_ubuntu_nano
+    run:
+      name: Install Nano text editor on Ubuntu
+      command: sudo apt-get install nano
+
+jobs:
+  rubocop_lint:
+    docker:
+      - image: circleci/ruby:2.5
+    working_directory: ~/pry
+    steps:
+      - checkout
+      - <<: *repo_save_cache
+      - <<: *bundle_install
+      - run:
+          name: Run RuboCop linting
+          command: bundle exec rubocop --parallel
+  yard_lint:
+    docker:
+      - image: circleci/ruby:2.5
+    working_directory: ~/pry
+    steps:
+      - checkout
+      - <<: *repo_save_cache
+      - <<: *bundle_install
+      - run:
+          name: Run YARD linting
+          command: bundle exec yardoc --fail-on-warning --no-progress
+  "ruby-1.9":
+    docker:
+      - image: kyrylo/ruby-1.9.3p551
+    working_directory: /home/circleci/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+  "ruby-2.0":
+    docker:
+      - image: kyrylo/ruby-2.0.0p648
+    working_directory: /home/circleci/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+  "ruby-2.1":
+    docker:
+      - image: circleci/ruby:2.1
+    working_directory: ~/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+  "ruby-2.2":
+    docker:
+      - image: circleci/ruby:2.2
+    working_directory: ~/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+  "ruby-2.3":
+    docker:
+      - image: circleci/ruby:2.3
+    working_directory: ~/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+  "ruby-2.4":
+    docker:
+      - image: circleci/ruby:2.4
+    working_directory: ~/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+  "ruby-2.5":
+    docker:
+      - image: circleci/ruby:2.5
+    working_directory: ~/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+  "jruby-9.1-jdk":
+    docker:
+      - image: circleci/jruby:9.1-jdk
+    working_directory: ~/pry
+    steps:
+      - <<: *repo_restore_cache
+      - <<: *bundle_install
+      - <<: *unit
+
+workflows:
+  version: 2
+  build:
+    jobs:
+      - rubocop_lint
+      - yard_lint
+      - "ruby-1.9":
+          requires:
+            - rubocop_lint
+            - yard_lint
+      - "ruby-2.0":
+          requires:
+            - rubocop_lint
+            - yard_lint
+      - "ruby-2.1":
+          requires:
+            - rubocop_lint
+            - yard_lint
+      - "ruby-2.2":
+          requires:
+            - rubocop_lint
+            - yard_lint
+      - "ruby-2.3":
+          requires:
+            - rubocop_lint
+            - yard_lint
+      - "ruby-2.4":
+          requires:
+            - rubocop_lint
+            - yard_lint
+      - "ruby-2.5":
+          requires:
+            - rubocop_lint
+            - yard_lint
+      - "jruby-9.1-jdk":
+          requires:
+            - rubocop_lint
+            - yard_lint