Add test workflow

.github/workflows/test.yml

@@ -0,0 +1,25 @@
+name: test
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test:
+    name: Run tests
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: '.nvmrc'
+      - name: Install dependencies
+        run: npm ci
+      - name: Test
+        run: npm test

README.md

@@ -1,4 +1,4 @@
-# GOV.UK Prototype Wizard
+# GOV.UK Prototype Wizard · [![test](https://github.com/x-govuk/govuk-prototype-wizard/actions/workflows/test.yml/badge.svg)](https://github.com/x-govuk/govuk-prototype-wizard/actions/workflows/test.yml)
 
 Build and iterate ‘one thing per page’ user journeys when prototyping GOV.UK services.