better testing: time()-function-mock

as discussed in #203
https://github.com/yiisoft/yii2/issues/203#issuecomment-17759631

tests/unit/framework/caching/CacheTest.php

@@ -1,5 +1,17 @@
 <?php
+
+namespace yii\caching;
+
+/**
+ * Mock for the time() function for caching classes
+ * @return int
+ */
+function time() {
+	return \yiiunit\framework\caching\CacheTest::$time ?: \time();
+}
+
 namespace yiiunit\framework\caching;
+
 use yiiunit\TestCase;
 use yii\caching\Cache;
 
@@ -9,6 +21,12 @@ use yii\caching\Cache;
 abstract class CacheTest extends TestCase
 {
 	/**
+	 * @var int virtual time to be returned by mocked time() function.
+	 * Null means normal time() behavior.
+	 */
+	public static $time;
+
+	/**
 	 * @return Cache
 	 */
 	abstract protected function getCacheInstance();
@@ -19,6 +37,11 @@ abstract class CacheTest extends TestCase
 		$this->mockApplication();
 	}
 
+	protected function tearDown()
+	{
+		static::$time = null;
+	}
+
 	/**
 	 * @return Cache
 	 */

tests/unit/framework/caching/DbCacheTest.php

@@ -1,5 +1,7 @@
 <?php
+
 namespace yiiunit\framework\caching;
+
 use yii\caching\DbCache;
 use yiiunit\TestCase;
 
@@ -70,4 +72,15 @@ class DbCacheTest extends CacheTest
 		}
 		return $this->_cacheInstance;
 	}
+
+	public function testExpire()
+	{
+		$cache = $this->getCacheInstance();
+
+		$this->assertTrue($cache->set('expire_test', 'expire_test', 2));
+		static::$time = time() + 1;
+		$this->assertEquals('expire_test', $cache->get('expire_test'));
+		static::$time = time() + 2;
+		$this->assertFalse($cache->get('expire_test'));
+	}
 }

tests/unit/framework/caching/FileCacheTest.php

@@ -22,4 +22,15 @@ class FileCacheTest extends CacheTest
 		}
 		return $this->_cacheInstance;
 	}
+
+	public function testExpire()
+	{
+		$cache = $this->getCacheInstance();
+
+		$this->assertTrue($cache->set('expire_test', 'expire_test', 2));
+		static::$time = time() + 1;
+		$this->assertEquals('expire_test', $cache->get('expire_test'));
+		static::$time = time() + 2;
+		$this->assertFalse($cache->get('expire_test'));
+	}
 }