Is it complicated to implement a NodeDriver for my application?

You may not actually need to do that. You can use one of the Node Drivers that work with any App, such as the FediverseManualNodeDriver or the FediverseSaasNodeDriver.

However: while it is great that they work with any App, they don’t provide much automation: instead, you will be prompted to manually perform the activities that haven’t be automated by a custom Node Driver for your App, such as:

• “Now create a user account on this instance”, or
• “As user example1 on this instance, make a post with the content ‘Good morning’”, or
• “As user example2 on the other instance, check that ‘Good morning’ has arrived in your inbox, and if so, enter ‘y”."

If this manual work doesn’t work for you – probably soon after entering the same info half a dozen times without an automated Node Driver for your App – you can implement a suitable Node Driver.

You can do this gradually and focus just on automating what is most time-consuming for you up to and including full automation.