Update workflow to run tests on all OSes

.github/workflows/dart.yaml

@@ -1,35 +1,40 @@
-name: Dart
-
-on:
-  schedule:
-    # “At 00:00 (UTC) on Sunday.”
-    - cron: '0 0 * * 0'
-  push:
-    branches: [ main ]
-  pull_request:
-    branches: [ main ]
-
-# Declare default permissions as read only.
 permissions: read-all
 
 jobs:
-  build:
+  analyze:
     runs-on: ubuntu-latest
 
     steps:
       # These are the latest versions of the github actions; dependabot will
       # send PRs to keep these up-to-date.
       - uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9
       - uses: dart-lang/setup-dart@d6a63dab3335f427404425de0fbfed4686d93c4f
+        with:
+          sdk: dev
 
       - name: Install dependencies
         run: dart pub get
-  
+
       - name: Verify formatting
         run: dart format --output=none --set-exit-if-changed .
 
       - name: Analyze project source
         run: dart analyze --fatal-infos
 
-      # - name: Run tests
-      #   run: dart test
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        sdk: dev
+    steps:
+      - uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9
+      - uses: dart-lang/setup-dart@d6a63dab3335f427404425de0fbfed4686d93c4f
+        with:
+          sdk: ${{ matrix.sdk }}
+
+      - name: Install dependencies
+        run: dart pub get
+
+      - name: Run tests
+        run: dart test