Do not analyse all detail of your user stories up-front for the next sprint. This is called a mini-waterfall.
Do not develop your user story and then test it. This is also called a mini-waterfall.
Do not split up all your user stories in the sprint planning in tasks. You cannot think of everything up-front. You only need to think of the important things to decide what it take s to put a story in your sprint.
“Considering Backlog Refinement as a “meeting” that includes only the Product Owner and the “Lead Developer”“. Zombie Scrum – Symptoms, Causes and Treatment.
Do as much as needed up-front, elaborate the stories gradually during your sprint and do it as a team. This is called swarming and building up a multi-functional team, where everybody helps each other to jointly reach the sprint goal.