test: improve process warning coverage

PR-URL: #15212
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

test/parallel/test-process-warning.js

@@ -0,0 +1,59 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+
+function test1() {
+  // Output is skipped if the argument to the 'warning' event is
+  // not an Error object.
+  common.hijackStderr(common.mustNotCall('stderr.write must not be called'));
+  process.emit('warning', 'test');
+  setImmediate(test2);
+}
+
+function test2() {
+  // Output is skipped if it's a deprecation warning and
+  // process.noDeprecation = true
+  process.noDeprecation = true;
+  process.emitWarning('test', 'DeprecationWarning');
+  process.noDeprecation = false;
+  setImmediate(test3);
+}
+
+function test3() {
+  common.restoreStderr();
+  // Type defaults to warning when the second argument is an object
+  process.emitWarning('test', {});
+  process.once('warning', common.mustCall((warning) => {
+    assert.strictEqual(warning.name, 'Warning');
+  }));
+  setImmediate(test4);
+}
+
+function test4() {
+  // process.emitWarning will throw when process.throwDeprecation is true
+  // and type is `DeprecationWarning`.
+  process.throwDeprecation = true;
+  assert.throws(
+    () => process.emitWarning('test', 'DeprecationWarning'),
+    /^DeprecationWarning: test$/);
+  process.throwDeprecation = false;
+  setImmediate(test5);
+}
+
+function test5() {
+  // Setting toString to a non-function should not cause an error
+  const err = new Error('test');
+  err.toString = 1;
+  process.emitWarning(err);
+  setImmediate(test6);
+}
+
+function test6() {
+  process.emitWarning('test', { detail: 'foo' });
+  process.on('warning', (warning) => {
+    assert.strictEqual(warning.detail, 'foo');
+  });
+}
+
+test1();