diff --git a/.dockerignore b/.dockerignore
new file mode 100644
index 00000000..07e8e4a2
--- /dev/null
+++ b/.dockerignore
@@ -0,0 +1 @@
+/dockerfiles/
diff --git a/.travis.yml b/.travis.yml
index 18547fec..1aa4598e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,10 +1,24 @@
----
-dist: xenial
-language: ruby
-cache: bundler
-rvm:
-  - 2.6
-env:
-  - PYENV_VERSION=3.7 PYTHON=python
-before_install:
-  - pip install --user matplotlib
+notifications:
+  webhooks:
+    - https://webhook.commit-email.info/
+
+services:
+  - docker
+
+matrix:
+  include:
+    - name: Ruby 2.6
+      env: TYPE=ruby-2.6
+
+install:
+  - docker build
+      -t red-data-tools/charty-${TYPE}
+      -f dockerfiles/Dockerfile.${TYPE}
+      .
+
+script:
+  - docker run
+      --interactive
+      --tty
+      red-data-tools/charty-${TYPE}
+      bundle exec rake
diff --git a/charty.gemspec b/charty.gemspec
index 7333de46..d7613690 100644
--- a/charty.gemspec
+++ b/charty.gemspec
@@ -26,14 +26,15 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
+  spec.add_development_dependency "activerecord"
   spec.add_development_dependency "bundler", ">= 1.16"
-  spec.add_development_dependency "rake"
-  spec.add_development_dependency "test-unit"
-  spec.add_development_dependency "numo-narray"
+  spec.add_development_dependency "daru"
+  spec.add_development_dependency "matplotlib"
   spec.add_development_dependency "nmatrix"
+  spec.add_development_dependency "numo-narray"
+  spec.add_development_dependency "rake"
   spec.add_development_dependency "red-datasets", ">= 0.0.9"
-  spec.add_development_dependency "daru"
-  spec.add_development_dependency "activerecord"
+  spec.add_development_dependency "red-opencv"
   spec.add_development_dependency "sqlite3"
-  spec.add_development_dependency "matplotlib"
+  spec.add_development_dependency "test-unit"
 end
diff --git a/dockerfiles/Dockerfile.ruby-2.6 b/dockerfiles/Dockerfile.ruby-2.6
new file mode 100644
index 00000000..9e1eeab1
--- /dev/null
+++ b/dockerfiles/Dockerfile.ruby-2.6
@@ -0,0 +1,41 @@
+FROM ruby:2.6
+
+RUN \
+  apt update && \
+  apt install -y \
+    apt-transport-https \
+    wget && \
+  wget -O /usr/share/keyrings/red-data-tools-keyring.gpg \
+    https://packages.red-data-tools.org/debian/red-data-tools-keyring.gpg && \
+  echo "deb [signed-by=/usr/share/keyrings/red-data-tools-keyring.gpg] https://packages.red-data-tools.org/debian/ buster main" > \
+    /etc/apt/sources.list.d/red-data-tools.list && \
+  apt update && \
+  apt install -y \
+    python3-pip \
+    sudo \
+    xvfb && \
+  gem install \
+    bundler \
+    rake && \
+  pip3 install \
+    matplotlib
+
+RUN \
+  useradd --user-group --create-home charty
+
+RUN \
+  echo "charty ALL=(ALL:ALL) NOPASSWD:ALL" | \
+    EDITOR=tee visudo -f /etc/sudoers.d/charty
+
+COPY . /home/charty/charty
+RUN chown -R charty:charty /home/charty/charty
+
+USER charty
+WORKDIR /home/charty/charty
+
+RUN bundle install
+
+CMD \
+  dbus-run-session \
+    xvfb-run --server-args "-screen 0 640x480x24" \
+    bundle exec rake
diff --git a/test/backends/pyplot/curve_integer.png b/test/backends/pyplot/curve_integer.png
new file mode 100644
index 00000000..48a9baff
Binary files /dev/null and b/test/backends/pyplot/curve_integer.png differ
diff --git a/test/backends/pyplot/curve_test.rb b/test/backends/pyplot/curve_test.rb
new file mode 100644
index 00000000..5d40fc14
--- /dev/null
+++ b/test/backends/pyplot/curve_test.rb
@@ -0,0 +1,23 @@
+require_relative "../../test_helper"
+
+class BackendsPyplotCurveTest < Test::Unit::TestCase
+  include Helper::Image
+
+  def setup
+    @plotter = Charty::Plotter.new(:pyplot)
+  end
+
+  def expected_image_path(*components)
+    File.join(__dir__, *components)
+  end
+
+  test("Integer") do
+    curve = @plotter.curve do
+      series [0, 1, 2, 3, 4], [10, 40, 20, 90, 70], label: "sample1"
+    end
+    output = Tempfile.new(["curve", ".png"])
+    curve.save(output.path)
+    assert_image(expected_image_path("curve_integer.png"),
+                 output.path)
+  end
+end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index bd9de9e6..63020348 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,3 +1,24 @@
 $LOAD_PATH.unshift File.expand_path('../../lib', __FILE__)
 require 'charty'
 require 'test/unit'
+require 'tempfile'
+begin
+  require 'cv'
+rescue LoadError
+end
+
+
+module Helper
+  module Image
+    def assert_image(expected_path, actual_path)
+      unless defined?(::CV)
+        omit("red-opencv is required for #{__method__}")
+      end
+      expected = CV::Image.read(expected_path)
+      actual = CV::Image.read(actual_path)
+      # TODO: Make this loose
+      assert_equal(expected.bytes.to_s,
+                   actual.bytes.to_s)
+    end
+  end
+end