fix(#252): stacktraces in different vm context

lib/layouts.js

@@ -30,7 +30,7 @@ const semver = require('semver');
 
 function wrapErrorsWithInspect(items) {
   return items.map((item) => {
-    if ((item instanceof Error) && item.stack) {
+    if (util.isError(item) && item.stack) {
       return {
         inspect: function () {
           return semver.satisfies(process.version, '>=6') ? util.format(item) : `${util.format(item)}\n${item.stack}`;

test/tap/stacktraces-test.js

@@ -0,0 +1,31 @@
+'use strict';
+
+const test = require('tap').test;
+
+test('Stacktraces from errors in different VM context', (t) => {
+  const log4js = require('../../lib/log4js');
+  const recorder = require('../../lib/appenders/recording');
+  const layout = require('../../lib/layouts').basicLayout;
+  const vm = require('vm');
+
+  log4js.configure({
+    appenders: { vcr: { type: 'recording' } },
+    categories: { default: { appenders: ['vcr'], level: 'debug' } }
+  });
+
+  const logger = log4js.getLogger();
+
+  try {
+    // Access not defined variable.
+    vm.runInNewContext('myVar();', {}, 'myfile.js');
+  } catch (e) {
+    // Expect to have a stack trace printed.
+    logger.error(e);
+  }
+
+  const events = recorder.replay();
+  // recording appender events do not go through layouts, so let's do it
+  const output = layout(events[0]);
+  t.match(output, 'stacktraces-test.js');
+  t.end();
+});