Fixed phpstan issues

tests/Composer/Test/DependencyResolver/PoolTest.php

@@ -65,6 +65,6 @@ class PoolTest extends TestCase
 
     protected function createPool()
     {
-        return new Pool(array('stable' => BasePackage::STABILITY_STABLE));
+        return new Pool();
     }
 }

tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php

@@ -27,7 +27,7 @@ class RuleSetIteratorTest extends TestCase
 
     protected function setUp()
     {
-        $this->pool = new Pool(array('stable' => BasePackage::STABILITY_STABLE));
+        $this->pool = new Pool();
 
         $this->rules = array(
             RuleSet::TYPE_JOB => array(

tests/Composer/Test/DependencyResolver/RuleSetTest.php

@@ -139,7 +139,7 @@ class RuleSetTest extends TestCase
 
     public function testPrettyString()
     {
-        $pool = new Pool(array('stable' => BasePackage::STABILITY_STABLE));
+        $pool = new Pool();
         $pool->setPackages(array(
             $p = $this->getPackage('foo', '2.1'),
         ));

tests/Composer/Test/DependencyResolver/RuleTest.php

@@ -93,7 +93,7 @@ class RuleTest extends TestCase
 
     public function testPrettyString()
     {
-        $pool = new Pool(array('stable' => BasePackage::STABILITY_STABLE));
+        $pool = new Pool();
         $pool->setPackages(array(
             $p1 = $this->getPackage('foo', '2.1'),
             $p2 = $this->getPackage('baz', '1.1'),