<p>Automated driving systems (ADSs) have made significant strides in recent years through the combined efforts of academia and industry. A typical ADS is composed of various complex modules, including perception, planning, and control. As emerging and complex computer programs, ADSs inevitably contain flaws, making it crucial to ensure their safety since any unsafe behavior can result in catastrophic outcomes. Testing is widely recognized as a key approach to ensuring ADS safety by uncovering unsafe behaviors. However, designing effective testing techniques for ADSs is exceptionally challenging due to the high complexity and multidisciplinary nature of these systems. Although an extensive body of literature focuses on ADS testing and several surveys summarizing technical advancements have been published, most concentrate on system-level testing performed within software simulators. Consequently, they often overlook the distinct characteristics, testing requirements, and datasets associated with various ADS modules. In this paper, we present a comprehensive survey of existing ADS testing literature. We begin by investigating the testing infrastructure for ADSs, including available datasets and tools, detailing their capabilities and characteristics. We then survey testing techniques for individual ADS modules (e.g., AI-based modules and firmware) and the integrated system, highlighting technical differences between validation layers. Finally, based on our findings, we identify key challenges and outline potential research opportunities in the field.</p>