ci: integration test against nokogiri, sqlite3, re2

.github/workflows/downstream.yml

@@ -18,7 +18,38 @@ on:
       - '*'
 
 jobs:
-  skeleton:
+  downstream:
+    name: downstream-${{matrix.name}}
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [ubuntu-latest, windows-latest, macos-latest]
+        include:
+          - url: https://github.com/mudge/re2
+            name: re2
+            command: "bundle exec rake compile spec"
+            ruby: "3.3"
+          - url: https://github.com/sparklemotion/nokogiri
+            name: nokogiri
+            command: "bundle exec rake compile test"
+            ruby: "3.3"
+          - url: https://github.com/sparklemotion/sqlite3-ruby
+            name: sqlite3
+            command: "bundle exec rake compile test"
+            ruby: "3.3"
     runs-on: ubuntu-latest
     steps:
-      - run: echo hello world
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{matrix.ruby}}
+          bundler-cache: true
+          bundler: latest
+      - run: git clone --depth=1 ${{matrix.url}} ${{matrix.name}}
+      - name: ${{matrix.name}} test suite
+        working-directory: ${{matrix.name}}
+        run: |
+          bundle remove mini_portile2 || true
+          bundle add mini_portile2 --path=".."
+          bundle install --local || bundle install
+          ${{matrix.command}}