Add passing unit tests

assets/hello.txt

@@ -0,0 +1 @@
+SGVsbG8gV29ybGQh

tests/new_unit_tests/Commands/ArtCommandTest.php

@@ -1,31 +1,26 @@
 <?php
-
 namespace Pantheon\Terminus\UnitTests\Commands;
 
-use Codeception\Specify;
-use Pantheon\Terminus\Commands\ArtCommand;
-use Pantheon\Terminus\Config;
-
+use Pantheon\Terminus\Tests\CommandTestCase;
+use Symfony\Component\Console\Output\BufferedOutput;
 
-/**
- * Testing class for Pantheon\Terminus\Terminus
- */
-class ArtCommandTest extends \PHPUnit_Framework_TestCase
+class ArtCommandTest extends CommandTestCase
 {
-    /**
-     * @var ArtCommand
-     */
-    private $command;
 
     public function setUp()
     {
-        $config = new Config([]);
-        $this->command = new ArtCommand();
-        $this->command->setConfig($config);
+        parent::setUp();
+        $this->setInput(['command' => 'art', 'name' => 'hello']);
     }
 
     public function testArtPrintsArt()
     {
-        assertEquals(file_get)
+        $this->assertEquals('Hello World!', $this->runCommand()->getOutput());
+    }
+
+    public function testArtRejectsNonExistantFiles()
+    {
+        $this->setInput(['command' => 'art', 'name' => 'foo']);
+        $this->assertEquals('Not a valid work of art!', $this->runCommand()->getOutput());
     }
 }