MAGETWO-43906: Long database prefix length breaks setup

- added test-case

Author: Ivan Gavryshko

setup/src/Magento/Setup/Test/Unit/Validator/DbValidatorTest.php

@@ -87,6 +87,18 @@ public function testCheckDatabaseTablePrefixWrongFormat()
         $this->assertEquals(true, $this->dbValidator->checkDatabaseTablePrefix('_wrong_format'));
     }
 
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage Table prefix length can't be more then
+     */
+    public function testCheckDatabaseTablePrefixWrongLength()
+    {
+        $this->assertEquals(
+            true,
+            $this->dbValidator->checkDatabaseTablePrefix('mvbXzXzItSIr0wrZW3gqgV2UKrWiK1Mj7bkBlW72rZW3gqgV2UKrWiK1M')
+        );
+    }
+
     /**
      * @expectedException \Magento\Setup\Exception
      * @expectedExceptionMessage Database connection failure.