"When interviewing for a scrum master position, make sure to showcase the interpersonal and managerial skills needed to excel in the dynamic environment of product management. Be prepared to answer a variety of situational questions that will assess your ability to manage a team of engineers, prioritize projects, and direct the scrum process. There are several different types of scrum certifications so make sure to research which is necessary for the position you are applying to."
What would you do if a developer wanted to do design and implementation in one sprint, and testing in another sprint
Don't allow this. Break down the User Story into smaller pieces that fit into one sprint again.