download Chromium only when tests are run

test/helper/download-chromium.js

@@ -0,0 +1,24 @@
+const packageJson = require('puppeteer-core/package.json');
+const puppeteer = require('puppeteer-core');
+
+const fetcher = puppeteer.createBrowserFetcher();
+const revision = packageJson.puppeteer.chromium_revision;
+
+/* eslint-disable no-console */
+module.exports = async () => {
+    const downloadedRevisions = await fetcher.localRevisions();
+    if (downloadedRevisions.indexOf(revision) !== -1) {
+        console.log('Chromium already downloaded');
+        return Promise.resolve();
+    }
+
+    console.log('Downloading Chromium...');
+    return fetcher.download(revision)
+        .then(() => {
+            console.log('Downloaded Chromium successfully');
+        })
+        .catch(error => {
+            console.error(error);
+            process.exit(1);
+        });
+};