[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/Connection/ConnectionExceptionTest.php

@@ -23,8 +23,12 @@ class ConnectionExceptionTest 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 $inner = null
+    ) {
         return new ConnectionException($connection, $message, $code, $inner);
     }
 }