Extract cache interface

Refactoring to allow for alternative cache implementations. Includes
implementations for the default noop (i.e. un-cached) behavior and a
filesystem-based cache whose configuration is consistent with the
existing Mustache_Engine constructor.

Includes updated and new tests.

test/Mustache/Test/Cache/FilesystemCacheTest.php

@@ -0,0 +1,58 @@
+<?php
+
+/**
+ * @group functional
+ */
+class Mustache_Test_Cache_FilesystemCacheTest extends PHPUnit_Framework_TestCase
+{
+    private static $tempDir;
+
+    public static function setUpBeforeClass()
+    {
+        self::$tempDir = sys_get_temp_dir() . '/mustache_test';
+        if (file_exists(self::$tempDir)) {
+            self::rmdir(self::$tempDir);
+        }
+    }
+
+    public function testCacheGetNone()
+    {
+        $key = 'some key';
+        $cache = new Mustache_Cache_FilesystemCache(self::$tempDir);;
+        $cached = $cache->get($key);
+
+        $this->assertNull($cached);
+    }
+
+    public function testCachePut()
+    {
+        $key = 'some key';
+        $value = 'some value';
+        $cache = new Mustache_Cache_FilesystemCache(self::$tempDir);;
+        $cache->put($key, $value);
+        $cached = $cache->get($key);
+
+        $this->assertEquals($cached, $value);
+    }
+
+    private static function rmdir($path)
+    {
+        $path = rtrim($path, '/').'/';
+        $handle = opendir($path);
+        while (($file = readdir($handle)) !== false) {
+            if ($file == '.' || $file == '..') {
+                continue;
+            }
+
+            $fullpath = $path.$file;
+            if (is_dir($fullpath)) {
+                self::rmdir($fullpath);
+            } else {
+                unlink($fullpath);
+            }
+        }
+
+        closedir($handle);
+        rmdir($path);
+    }
+}

test/Mustache/Test/EngineTest.php

@@ -58,6 +58,7 @@ class Mustache_Test_EngineTest extends PHPUnit_Framework_TestCase
         $this->assertTrue($mustache->hasHelper('foo'));
         $this->assertTrue($mustache->hasHelper('bar'));
         $this->assertFalse($mustache->hasHelper('baz'));
+        $this->assertInstanceOf('Mustache_Cache_FilesystemCache', $mustache->getCache());
     }
 
     public static function getFoo()
@@ -95,6 +96,7 @@ class Mustache_Test_EngineTest extends PHPUnit_Framework_TestCase
         $parser    = new Mustache_Parser;
         $compiler  = new Mustache_Compiler;
         $mustache  = new Mustache_Engine;
+        $cache     = new Mustache_Cache_FilesystemCache(sys_get_temp_dir());
 
         $this->assertNotSame($logger, $mustache->getLogger());
         $mustache->setLogger($logger);
@@ -119,6 +121,10 @@ class Mustache_Test_EngineTest extends PHPUnit_Framework_TestCase
         $this->assertNotSame($compiler, $mustache->getCompiler());
         $mustache->setCompiler($compiler);
         $this->assertSame($compiler, $mustache->getCompiler());
+
+        $this->assertNotSame($cache, $mustache->getCache());
+        $mustache->setCache($cache);
+        $this->assertSame($cache, $mustache->getCache());
     }
 
     /**
@@ -134,10 +140,8 @@ class Mustache_Test_EngineTest extends PHPUnit_Framework_TestCase
         $source    = '{{ foo }}';
         $template  = $mustache->loadTemplate($source);
         $className = $mustache->getTemplateClassName($source);
-        $fileName  = self::$tempDir . '/' . $className . '.php';
+
         $this->assertInstanceOf($className, $template);
-        $this->assertFileExists($fileName);
-        $this->assertContains("\nclass $className extends Mustache_Template", file_get_contents($fileName));
     }
 
     /**
@@ -290,7 +294,7 @@ class Mustache_Test_EngineTest extends PHPUnit_Framework_TestCase
         $result = $mustache->render('{{ foo }}', array('foo' => 'FOO'));
         $this->assertEquals('FOO', $result);
 
-        $this->assertContains('WARNING: Template cache disabled, evaluating', file_get_contents($name));
+        $this->assertContains('WARNING: Template cache disabled', file_get_contents($name));
     }
 
     public function testLoggingIsNotTooAnnoying()