public function flushRemovesAllCacheEntries()
{
$backend = $this->setUpBackend();
$data = 'some data' . microtime();
$backend->set('BackendAPCTest1', $data);
$backend->set('BackendAPCTest2', $data);
$backend->set('BackendAPCTest3', $data);
$backend->flush();
$this->assertFalse($backend->has('BackendAPCTest1'), 'BackendAPCTest1');
$this->assertFalse($backend->has('BackendAPCTest2'), 'BackendAPCTest2');
$this->assertFalse($backend->has('BackendAPCTest3'), 'BackendAPCTest3');
}