Use GitHub Actions for CI

.github/workflows/ubuntu.yml

@@ -0,0 +1,62 @@
+name: CI
+
+on:
+- push
+- pull_request
+
+jobs:
+  test:
+    name: Test
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+        - ubuntu-20.04
+        - ubuntu-latest
+        ruby:
+        - 3.0
+        - 2.7
+        - 2.6
+        - 2.5
+        - 2.4
+        - 2.3
+        - debug
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 1
+
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+
+    - name: Install requirements on ubuntu
+      run: |
+        sudo apt install -y --no-install-recommends \
+                 libczmq-dev \
+                 python3 \
+                 python3-pip \
+                 python3-setuptools
+        sudo pip3 install wheel
+        sudo pip3 install -r ci/requirements.txt
+
+    - run: gem install bundler
+
+    - run: bundle install --jobs 4 --retry 3
+
+    - name: Run tests
+      env:
+        PYTHON: python3
+        ADAPTERS: cztop ffi-rzmq pyzmq
+      run: |
+        for adapter in $ADAPTERS; do
+          export IRUBY_TEST_SESSION_ADAPTER_NAME=$adapter
+          bundle exec rake test TESTOPTS=-v
+        done
+
+    - run: rake build
+
+    - run: gem install pkg/*.gem