Adding Twig_Environment::clearCacheFiles() to clear cache files that twig makes.

Refactoring test cases in previous commit.  Adding more tests for clearing cache files.
Fixes #192

lib/Twig/Environment.php

@@ -32,6 +32,7 @@ class Twig_Environment
     protected $strictVariables;
     protected $unaryOperators;
     protected $binaryOperators;
+    protected $templateClassPrefix = '__TwigTemplate_';
 
     /**
      * Constructor.
@@ -187,7 +188,7 @@ class Twig_Environment
      */
     public function getTemplateClass($name)
     {
-        return '__TwigTemplate_'.md5($this->loader->getCacheKey($name));
+        return $this->templateClassPrefix.md5($this->loader->getCacheKey($name));
     }
 
     /**
@@ -229,6 +230,23 @@ class Twig_Environment
         $this->loadedTemplates = array();
     }
 
+    /**
+     * Clears the template cache files on the filesystem.
+     *
+     * @return boolean success
+     */
+    public function clearCacheFiles()
+    {
+        if ($this->cache) {
+            foreach(new DirectoryIterator($this->cache) as $fileInfo) {
+                if (strpos($fileInfo->getFilename(), $this->templateClassPrefix) === 0) {
+                    @unlink($fileInfo->getPathname());
+                }
+            }
+        }
+        return true;
+    }
+
     public function getLexer()
     {
         if (null === $this->lexer) {

test/Twig/Tests/FileCachingTest.php

@@ -4,6 +4,7 @@ class Twig_Tests_FileCachingTest extends PHPUnit_Framework_TestCase
 {
     protected $fileName;
     protected $tmpDir;
+    protected $env;
 
     function setUp()
     {
@@ -11,21 +12,30 @@ class Twig_Tests_FileCachingTest extends PHPUnit_Framework_TestCase
         if (!is_writable($this->tmpDir)) {
             $this->markTestSkipped(sprintf('Cannot write to %s, cannot test file caching.', $this->tmpDir));
         }
+        $this->env = new Twig_Environment(new Twig_Loader_String(), array('cache' => $this->tmpDir));
         parent::setUp();
     }
     
     function testWritingCacheFiles()
     {
-        $loader = new Twig_Loader_String();
-        $env = new Twig_Environment($loader, array('cache' => $this->tmpDir));
-
         $name = 'This is just text.';
-        $template = $env->loadTemplate($name);
-        $cacheFileName = $env->getCacheFilename($name);
+        $template = $this->env->loadTemplate($name);
+        $cacheFileName = $this->env->getCacheFilename($name);
 
         $this->assertTrue(file_exists($cacheFileName), 'Cache file does not exist.');
         $this->fileName = $cacheFileName;
     }
+    
+    function testClearingCacheFiles()
+    {
+        $name = 'I will be deleted.';
+        $template = $this->env->loadTemplate($name);
+        $cacheFileName = $this->env->getCacheFilename($name);
+
+        $this->assertTrue(file_exists($cacheFileName), 'Cache file does not exist.');
+        $this->assertTrue($this->env->clearCacheFiles());
+        $this->assertFalse(file_exists($cacheFileName), 'Cache file was not cleared.');
+    }
 
     function tearDown()
     {