Add parallel test.

test/recipe/Helper/RecipeTester.php

@@ -79,10 +79,14 @@ abstract class RecipeTester extends \PHPUnit_Framework_TestCase
      * Execute command with tester.
      *
      * @param string $command
+     * @param array $args
+     * @param array $options
+     * @return string Display result.
      */
-    protected function exec($command)
+    protected function exec($command, $args = [], $options = [])
     {
-        $this->tester->run(['command' => $command]);
+        $this->tester->run(['command' => $command] + $args, $options);
+        return $this->tester->getDisplay();
     }
 
     /**

test/src/Executor/Fixture/recipe.php

@@ -0,0 +1,9 @@
+<?php
+
+localServer('localhost');
+localServer('server1');
+localServer('server2');
+
+task('test', function () {
+    writeln('Hello world!');
+});

test/src/Executor/ParallelExecutorTest.php

@@ -0,0 +1,33 @@
+<?php
+/* (c) Anton Medvedev <anton@elfet.ru>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Deployer\Executor;
+
+use Deployer\Helper\RecipeTester;
+
+class ParallelExecutorTest extends RecipeTester
+{
+    /**
+     * Load or describe recipe.
+     *
+     * @return void
+     */
+    protected function loadRecipe()
+    {
+        include __DIR__ . '/Fixture/recipe.php';
+    }
+
+    public function testParallel()
+    {
+        define('DEPLOYER_BIN', __DIR__ . '/../../../bin/dep');
+        
+        $display = $this->exec('test', ['--parallel' => true, '--file' => __DIR__ . '/Fixture/recipe.php']);
+
+        $this->assertContains('Ok', $display);
+    }
+}
+