[tests] Replace deprecated TestCase::at().

The "at" matcher will be removed in PHPUnit 10 but it is not a bad thing
after all because it was cumbersome and error-prone.

Took the opportunity to improve some tests while converting them.

tests/Predis/Connection/FactoryTest.php

@@ -304,15 +304,14 @@ class FactoryTest extends PredisTestCase
             ->method('getParameters')
             ->willReturn($parameters);
         $connection
-            ->expects($this->at(1))
+            ->expects($this->exactly(2))
             ->method('addConnectCommand')
-            ->with($this->isRedisCommand('AUTH', array('foobar')));
-        $connection
-            ->expects($this->at(2))
-            ->method('addConnectCommand')
-            ->with($this->isRedisCommand('SELECT', array(0)));
+            ->withConsecutive(
+                array($this->isRedisCommand('AUTH', array('foobar'))),
+                array($this->isRedisCommand('SELECT', array('0')))
+            );
 
-            $factory = new Factory();
+        $factory = new Factory();
 
         // TODO: using reflection to make a protected method accessible :facepalm:
         $reflection = new \ReflectionObject($factory);