Inline condition and fix skip check.

src/Cache/Engine/MemcachedEngine.php

@@ -174,7 +174,7 @@ class MemcachedEngine extends CacheEngine
 
         if ($this->_config['username'] !== null && $this->_config['password'] !== null) {
             $sasl = method_exists($this->_Memcached, 'setSaslAuthData');
-            if (!$sasl) {
+            if (!method_exists($this->_Memcached, 'setSaslAuthData')) {
                 throw new InvalidArgumentException(
                     'Memcached extension is not built with SASL support'
                 );

tests/TestCase/Cache/Engine/MemcachedEngineTest.php

@@ -345,7 +345,7 @@ class MemcachedEngineTest extends TestCase
     public function testSaslAuthException()
     {
         $this->skipIf(
-            method_exists('setSaslAuthData', Memcached::class),
+            method_exists(Memcached::class, 'setSaslAuthData'),
             'Cannot test exception when sasl has been compiled in.'
         );
         $MemcachedEngine = new MemcachedEngine();