Add jest tests and CI workflow

.github/workflows/ci.yml

@@ -0,0 +1,17 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 18
+      - run: npm install
+      - run: npm test