Successful payment processing with different methods is essential for a positive user experience. Testing the shopping cart and checkout process ensures a smooth and error-free transaction for customers.

Functional testing is typically performed during the testing phase of the SDLC, where the application's functionality is systematically tested.

Risk management in testing should be an ongoing and iterative process throughout the project. It involves continuous identification, assessment, and mitigation of risks to adapt to changing circumstances and ensure that the testing process remains effective and aligned with project goals.

Code coverage is not typically considered as a metric in performance testing. Performance metrics focus on aspects like response time, throughput, and resource utilization (such as memory usage) to evaluate how well the system performs under different conditions. Code coverage is more relevant to functional testing.

The Test Case Traceability Matrix (TCTM) is a document that establishes a link between the requirements and test cases. It ensures that each requirement has corresponding test cases and vice versa.

The primary purpose of writing test cases is to document how to test the software, specifying inputs, expected outcomes, and conditions for executing tests.

Exploratory testing involves testers designing and executing test cases simultaneously based on their domain knowledge, intuition, and previous testing experience, making it a characteristic of exploratory testing in functional testing.

In complex systems, defining comprehensive use cases can be challenging, leading to potential gaps in testing coverage. Testing variations may be limited, and inadequate tools may hinder the ability to handle complex scenarios effectively. Additionally, the complexity increases the risk of overlooking critical system interactions, emphasizing the importance of thorough planning and execution in Use Case Testing for complex software systems.

Synthetic test data, designed to mimic real-world scenarios, is often most appropriate for compatibility testing. It allows thorough coverage of different database systems without exposing sensitive production data.

Security considerations should ideally be integrated during the Requirements Phase of the SDLC. This ensures that security requirements are identified and incorporated into the system design and development, establishing a strong foundation for building a secure software product from the early stages of the development life cycle.