Add contract for createPlatform()'s return type

tests/Doctrine/Tests/DBAL/Platforms/AbstractPostgreSqlPlatformTestCase.php

@@ -2,6 +2,7 @@
 
 namespace Doctrine\Tests\DBAL\Platforms;
 
+use Doctrine\DBAL\Platforms\AbstractPlatform;
 use Doctrine\DBAL\Platforms\PostgreSqlPlatform;
 use Doctrine\DBAL\Schema\Column;
 use Doctrine\DBAL\Schema\ColumnDiff;
@@ -20,6 +21,11 @@ abstract class AbstractPostgreSqlPlatformTestCase extends AbstractPlatformTestCa
     /** @var PostgreSqlPlatform */
     protected $platform;
 
+    /**
+     * @return PostgreSqlPlatform
+     */
+    abstract public function createPlatform() : AbstractPlatform;
+
     public function getGenerateTableSql() : string
     {
         return 'CREATE TABLE test (id SERIAL NOT NULL, test VARCHAR(255) DEFAULT NULL, PRIMARY KEY(id))';