Canary test workflow, checks that key downstream packages still build

.github/workflows/main.yml

@@ -3,8 +3,8 @@ on:
   - pull_request
   - push
 jobs:
-  main:
-    name: '${{matrix.node}} on ${{matrix.os}}'
+  test:
+    name: test / micromark / ${{matrix.node}} on ${{matrix.os}}
     runs-on: ${{matrix.os}}
     steps:
       - uses: actions/checkout@v2
@@ -23,3 +23,46 @@ jobs:
         node:
           - lts/erbium
           - node
+  canary:
+    name: canary / ${{matrix.package}} / ${{matrix.node}} on ${{matrix.os}}
+    runs-on: ${{matrix.os}}
+    steps:
+      - name: checkout micromark
+        uses: actions/checkout@v2
+      - name: setup node
+        uses: dcodeIO/setup-node-nvm@master
+        with:
+          node-version: ${{matrix.node}}
+      - name: setup micromark
+        run: |
+          npm install -g npm
+          npm install
+          npm run build
+      - name: checkout ${{matrix.package}}
+        uses: actions/checkout@v2
+        with:
+          repository: ${{matrix.package}}
+          path: canary/${{matrix.package}}
+      - name: test ${{matrix.package}}
+        run: |
+          npm install
+          for package in $(ls ../../packages); do
+            npx rimraf "node_modules/**/$package"
+          done
+          npm test
+        working-directory: canary/${{matrix.package}}
+    strategy:
+      fail-fast: false
+      max-parallel: 2
+      matrix:
+        os:
+          - ubuntu-latest
+        node:
+          - node
+        package:
+          - micromark/micromark-extension-gfm
+          - micromark/micromark-extension-directive
+          - micromark/micromark-extension-mdx
+          - syntax-tree/mdast-util-from-markdown
+          - remarkjs/remark
+          - remarkjs/react-markdown