Add npm test script

Author: andreslucena

.github/workflows/ci_antora.yml

@@ -19,6 +19,6 @@ jobs:
           node-version: '14.x'
       - name: Install dependencies
         run: npm install
-      - name: Run build script
-        run: npm run build
+      - name: Run test script
+        run: npm test
 

package.json

@@ -2,7 +2,8 @@
   "name": "decidim-documentation",
   "private": true,
   "scripts": {
-    "build": "antora antora-playbook.yml $@"
+    "build": "antora antora-playbook.yml $@",
+    "test": "errlog=$(mktemp) && npm run build &2> $errlog && if [ -e $errlog ] ; then exit 1 ; else exit 0 ; fi"
   },
   "devDependencies": {
     "@antora/cli": "^3.0.0",