In most instances, the adventure operator will be happy to help the group obtain a COVID-19 test prior to the end of the adventure. Because this is an entry requirement for most travellers when they return home. The operators are taking this into account and will often schedule a time for the entire group to go to a testing facility together. The best thing to do is speak to your guide at the start of the adventure and he/she will be able to let you know the process and assist you with booking a test if this isn't done by the operator themselves.
If you'd like more information before travelling, simply send a message on your Booking Conversation Page with any questions you have around COVID testing and the adventure operator will send you more details directly.