We would strongly recommend implementing this extension in a development environment before putting it live.
You need to set up the Woocommerce store to use the test account details.
You can then use the following test-card numbers to make sure that a transaction fully completes.
Card number 4444 3333 2222 1111
Expiry Date 08/2018
Card number 5555 4444 3333 1111
Expiry Date 08//2018
More cards can be found here.