test: add child_process.exec() timeout coverage

This commit adds coverage for the timeout option used by
child_process exec() and execFile().

PR-URL: https://github.com/nodejs/node/pull/9208
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

test/parallel/test-child-process-exec-timeout.js

@@ -0,0 +1,45 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const cp = require('child_process');
+
+if (process.argv[2] === 'child') {
+  setTimeout(() => {
+    // The following console statements are part of the test.
+    console.log('child stdout');
+    console.error('child stderr');
+  }, common.platformTimeout(1000));
+  return;
+}
+
+const cmd = `${process.execPath} ${__filename} child`;
+
+// Test the case where a timeout is set, and it expires.
+cp.exec(cmd, { timeout: 1 }, common.mustCall((err, stdout, stderr) => {
+  assert.strictEqual(err.killed, true);
+  assert.strictEqual(err.code, null);
+  assert.strictEqual(err.signal, 'SIGTERM');
+  assert.strictEqual(err.cmd, cmd);
+  assert.strictEqual(stdout.trim(), '');
+  assert.strictEqual(stderr.trim(), '');
+}));
+
+// Test with a different kill signal.
+cp.exec(cmd, {
+  timeout: 1,
+  killSignal: 'SIGKILL'
+}, common.mustCall((err, stdout, stderr) => {
+  assert.strictEqual(err.killed, true);
+  assert.strictEqual(err.code, null);
+  assert.strictEqual(err.signal, 'SIGKILL');
+  assert.strictEqual(err.cmd, cmd);
+  assert.strictEqual(stdout.trim(), '');
+  assert.strictEqual(stderr.trim(), '');
+}));
+
+// Test the case where a timeout is set, but not expired.
+cp.exec(cmd, { timeout: 2 ** 30 }, common.mustCall((err, stdout, stderr) => {
+  assert.ifError(err);
+  assert.strictEqual(stdout.trim(), 'child stdout');
+  assert.strictEqual(stderr.trim(), 'child stderr');
+}));