Distributed systems underpin modern computing, enabling powerful, reliable, and flexible operations across domains such as cloud computing, big data, and IoT. However, their complexity often leads to code defects that threaten usability, robustness, and security, making testing and defect detection essential. Dynamic testing, which evaluates systems during runtime, plays a key role in uncovering defects and assessing functionality. This paper introduces a four-layer bug threat model for distributed systems, covering system configuration, user requests, node communication, and environmental faults. Based on this model, it analyzes the challenges of testing distributed systems and proposes a general framework for dynamic testing. The paper highlights critical techniques such as multidimensional test input generation, system-critical state awareness, and defect judgment criteria. Additionally, the paper reviews popular dynamic testing tools and evaluates their effectiveness in defect discovery and test coverage. The findings show that multidimensional input generation significantly enhances testing efficiency. Finally, the paper discusses emerging trends and future directions in dynamic testing of distributed systems, aiming to address their inherent challenges and improve testing outcomes.