Add test case for countdown

test/fixtures/failcounter.js

@@ -0,0 +1,2 @@
+const Countdown = require('../common/countdown');
+new Countdown(2, () => {});

test/parallel/test-common-countdown.js

@@ -1,15 +1,33 @@
 'use strict';
 
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 const Countdown = require('../common/countdown');
+const fixtures = require('../common/fixtures');
+const { execFile } = require('child_process');
 
 let done = '';
-
 const countdown = new Countdown(2, () => done = true);
 assert.strictEqual(countdown.remaining, 2);
 countdown.dec();
 assert.strictEqual(countdown.remaining, 1);
 countdown.dec();
 assert.strictEqual(countdown.remaining, 0);
 assert.strictEqual(done, true);
+
+const failFixtures = [
+  [
+    fixtures.path('failcounter.js'),
+    'Mismatched <anonymous> function calls. Expected exactly 1, actual 0.',
+  ]
+];
+
+for (const p of failFixtures) {
+  const [file, expected] = p;
+  execFile(process.argv[0], [file], common.mustCall((ex, stdout, stderr) => {
+    assert.ok(ex);
+    assert.strictEqual(stderr, '');
+    const firstLine = stdout.split('\n').shift();
+    assert.strictEqual(firstLine, expected);
+  }));
+}