Add test workflow

.github/workflows/test.yml

@@ -0,0 +1,27 @@
+name: Run tests
+
+on:
+  [push]
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+
+    strategy:
+      matrix:
+        ruby-version: ['2.7', '3.0', '3.1']
+
+    steps:
+    - uses: actions/checkout@v3
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true
+
+    - name: Run tests
+      run: bundle exec rake