Integration testing and system testing are two important testing phases in software development. They verify different aspects of the software system at different levels and stages. The following explains their application scenarios in detail:

　　1. Integration Testing:
　　1. Module Integration Phase:
　　(1) Scenario: During the software development process, different modules need to be integrated into a whole after unit testing. Integration testing verifies the interaction and integration between modules at this stage.

　　(2) Objective: To ensure that the various modules can interact, communicate, and collaborate correctly when combined together without causing inconsistencies or conflicts.

　　2. Interface testing:
　　(1) Scenario: When different systems, services or components communicate through interfaces, integration testing is used to verify the correctness and reliability of the interfaces.

　　(2) Objective: Confirm that the interface can transfer and interact with data as expected and can handle various input and output situations.

　　3. Parallel and concurrent testing:
　　(1) Scenario: For software that supports multi-tasking or parallel operation, integration testing is used to verify these functions.

　　(2) Goal: Ensure that the system responds correctly and avoids conflicts and resource competition when executing multiple tasks or threads simultaneously.

　　4. Data consistency and error handling:
　　(1) Scenario: During the system integration phase, it is necessary to ensure that each module processes data in a consistent manner and can correctly handle various exceptions.

　　(2) Objective: To verify the accuracy, integrity, and security of data transmission and processing between modules, as well as the system's ability to handle and recover from errors.

　　2. System Testing:
　　1. Overall system verification:
　　(1) Scenario: The final stage of software development, during which the entire system is comprehensively tested, including functionality, performance, and user experience.

　　(2) Objective: To verify whether the system meets user needs and expectations, including whether the functions are complete, the performance is stable, and the user experience is good.

　　2. Functional testing:
　　(1) Scenario: Test whether the various functions of the system work normally as required by the requirements specification.

　　(2) Objective: To verify whether all functions of the system are correctly implemented according to the design requirements, including normal functions and functions under boundary conditions.

　　3. Performance testing:
　　(1) Scenario: Test the performance, stability and load capacity of the system.

　　(2) Objective: Confirm whether the system's response time, throughput, resource utilization and other indicators under different loads meet expectations and identify performance bottlenecks.

　　4. Security and reliability testing:
　　(1) Scenario: Verify the security of the system, including data security, user authentication, permission management, etc.

　　(2) Objective: Ensure the system's ability to resist unauthorized access and attacks, and ensure the system's reliability and stability in the face of abnormal situations.

　　5. User acceptance testing:
　　(1) Scenario: Testing is performed by end users or people representing users to confirm whether the system meets user expectations and needs.

　　(2) Objective: Confirm whether the system meets user expectations, including interface friendliness, ease of use, and compliance with business processes.

　　Integration testing and system testing are both important links in ensuring the quality of software systems. During the software development process, they complement each other and jointly ensure the stability, reliability and security of the system.