add tests for CommandExecutor.

Tests/PHPCI/Helper/CommandExecutorTest.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace PHPCI\Plugin\Tests\Helper;
+
+use PHPCI\Helper\CommandExecutor;
+use \Prophecy\PhpUnit\ProphecyTestCase;
+
+class CommandExecutorTest extends ProphecyTestCase
+{
+    /**
+     * @var CommandExecutor
+     */
+    protected $testedExecutor;
+
+    protected function setUp()
+    {
+        parent::setUp();
+        $mockBuildLogger = $this->prophesize('\PHPCI\BuildLogger');
+        $this->testedExecutor = new CommandExecutor($mockBuildLogger->reveal());
+    }
+
+    public function testGetLastOutput_ReturnsOutputOfCommand()
+    {
+        $this->testedExecutor->executeCommand(array('echo "%s"', 'Hello World'));
+        $output = $this->testedExecutor->getLastOutput();
+        $this->assertEquals("Hello World", $output);
+    }
+
+    public function testGetLastOutput_ForgetsPreviousCommandOutput()
+    {
+        $this->testedExecutor->executeCommand(array('echo "%s"', 'Hello World'));
+        $this->testedExecutor->executeCommand(array('echo "%s"', 'Hello Tester'));
+        $output = $this->testedExecutor->getLastOutput();
+        $this->assertEquals("Hello Tester", $output);
+    }
+}