mysqldump: Got error: 1017: Can't find file: 'drupal_install_test' (errno: 2) when using LOCK TABLES
You apparently have a missing drupal_install_test in your database schema. As the name says, it's a test table that is created at installation time to test the performance of the database and of the database user you provided for your site. At the end of the installation process, it gets dropped from the database.

The problem here is that the table has been dropped but mysql still thinks it exists. The reason why that table has remained in information_schema.tables should definitely be investigated and may reflect some issues in the database or in your server's configuration.

That said, if drupal_install_test is the only corrupted table in your database, you can try and drop it and proceed with your backup. I recommend that you make a full backup of the mysql data directory (in a typical linux installation /var/lib/mysql) and issue a DROP TABLE drupal_install_test command. Mysql should be able to restore the integrity of the schema tables and you should be able to proceed with your backup.