test: improve expectWarning error message

expectWarning() fails with a TypeError and a message about undefined not
being iterable when the warning is emitted more times than expected.
This change produces a more useful error message.

Refs: https://github.com/nodejs/node/pull/41307/files#r775197738

PR-URL: https://github.com/nodejs/node/pull/41326
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/common/index.js

@@ -549,7 +549,11 @@ function _expectWarning(name, expected, code) {
     expected.forEach(([_, code]) => assert(code, expected));
   }
   return mustCall((warning) => {
-    const [ message, code ] = expected.shift();
+    const expectedProperties = expected.shift();
+    if (!expectedProperties) {
+      assert.fail(`Unexpected extra warning received: ${warning}`);
+    }
+    const [ message, code ] = expectedProperties;
     assert.strictEqual(warning.name, name);
     if (typeof message === 'string') {
       assert.strictEqual(warning.message, message);

test/parallel/test-common-expect-warning.js

@@ -0,0 +1,50 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { spawn } = require('child_process');
+
+if (process.argv[2] !== 'child') {
+  // Expected error not emitted.
+  {
+    const child = spawn(
+      process.execPath, [__filename, 'child', 0], { encoding: 'utf8' }
+    );
+    child.on('exit', common.mustCall((status) => {
+      assert.notStrictEqual(status, 0);
+    }));
+  }
+
+  // Expected error emitted.
+  {
+    const child = spawn(
+      process.execPath, [__filename, 'child', 1], { encoding: 'utf8' }
+    );
+    child.on('exit', common.mustCall((status) => {
+      assert.strictEqual(status, 0);
+    }));
+  }
+
+  // Expected error emitted too many times.
+  {
+    const child = spawn(
+      process.execPath, [__filename, 'child', 2], { encoding: 'utf8' }
+    );
+    child.stderr.setEncoding('utf8');
+
+    let stderr = '';
+    child.stderr.on('data', (data) => {
+      stderr += data;
+    });
+    child.on('exit', common.mustCall((status) => {
+      assert.notStrictEqual(status, 0);
+      assert.match(stderr, /Unexpected extra warning received/);
+    }));
+  }
+} else {
+  const iterations = +process.argv[3];
+  common.expectWarning('fhqwhgads', 'fhqwhgads', 'fhqwhgads');
+  for (let i = 0; i < iterations; i++) {
+    process.emitWarning('fhqwhgads', 'fhqwhgads', 'fhqwhgads');
+  }
+}