tests: improve puppeteer's console logging

Author: darwin

test/resources/puppeteer.js

@@ -14,14 +14,28 @@ const serverOptions = {root: path};
 
 const server = httpServer.createServer(serverOptions);
 
+// see https://github.com/puppeteer/puppeteer/issues/3397#issuecomment-434970058
+async function logMsg(msg) {
+  // serialize my args the way I want
+  const args = await Promise.all(msg.args().map(arg => arg.executionContext().evaluate(arg => {
+    // I'm in a page context now. If my arg is an error - get me its message.
+    if (arg instanceof Error)
+      return arg.message;
+    // return arg right away. since we use `executionContext.evaluate`, it'll return JSON value of
+    // the argument if possible, or `undefined` if it fails to stringify it.
+    return arg;
+  }, arg)));
+  console.log(...args);
+}
+
 server.listen(port, host, function () {
-  console.log(`Server running at http://${host}:${port}/`);
+  console.log(`[puppeteer] Server running at http://${host}:${port}/`);
 
   (async () => {
     const browser = await puppeteer.launch();
     const page = await browser.newPage();
-    page.on('console', msg => console.log(msg.text()));
-    console.log("navigating to: ", url);
+    page.on('console', logMsg);
+    console.log("[puppeteer] Navigating to: ", url);
     await page.goto(url);
 
     const failures = await page.evaluate(() => {