I am a Scrum Master for a team consist of developers and testers. We are currently following 3 weeks Sprint. In my team testers don't want to any development and the developers don't want to involve in regression testing. Because of this situation below scenarios arise.
1. At the beginning of the Sprint, testers are creating test cases but they are releatively free
2. During the last week of the sprint, testers are busy with regression testing and developers are relatively free. Sometimes, the developers start to look into the US planned for next Sprint.