As you can see from the article [Kassa Compleet] How to programmatically get the list of available payment options for a merchant?, the official extension for Magento 1.x allows only the iDEAL payment option in the test mode:
But Kassa Compleet states, that the bank transfers payments are also allowed in the test mode:
So, why the official extension for Magento 1.x does not allow the «bank transfer» payment option in the test mode?