[tests] Start improving test suite.

- Make use of more typehints for function parameters
- Make use of typehints for function return values
- Use @var where needed to give proper hints to IDEs and avoid warnings
- Replace MockObject::setMethods() with addMethods() and onlyMethods()
- Rewording of some phpdocs

tests/Predis/Protocol/ProtocolExceptionTest.php

@@ -13,6 +13,7 @@ namespace Predis\Protocol;
 
 require_once __DIR__.'/../CommunicationExceptionTest.php';
 
+use Predis\CommunicationException;
 use Predis\CommunicationExceptionTest;
 use Predis\Connection\NodeConnectionInterface;
 
@@ -24,8 +25,12 @@ class ProtocolExceptionTest extends CommunicationExceptionTest
     /**
      * {@inheritdoc}
      */
-    protected function getException(NodeConnectionInterface $connection, $message, $code = 0, \Exception $inner = null)
-    {
+    protected function getException(
+        NodeConnectionInterface $connection,
+        string $message,
+        int $code = 0,
+        \Exception $inner = null
+    ): CommunicationException {
         return new ProtocolException($connection, $message, $code, $inner);
     }
 }