When writing test cases, what is the main difference between test cases designed for integration testing and those designed for system testing in a software project?

Introduction / Context:
Integration testing and system testing are two important levels in the testing hierarchy. Although both involve combining pieces of the software, they have different scopes and objectives. Understanding how test cases differ between these levels helps testers design the right kind of checks at the right time instead of repeating the same tests at multiple stages.

Given Data / Assumptions:

The software system is developed in modules or components that interact through defined interfaces.
Integration testing happens after unit testing and before full system testing.
System testing validates the complete integrated system against requirements and business scenarios.

Concept / Approach:
Integration test cases are driven mainly by the software architecture and design. They verify that modules communicate correctly, that data passed across interfaces is consistent and that error handling between components works as expected. System test cases are more user oriented and requirement oriented. They follow realistic end-to-end flows, including multiple modules, databases, external systems and user interfaces to confirm that the entire system fulfils its specified requirements.

Step-by-Step Solution:
Identify the goal of integration testing: to ensure that modules that have already been unit tested work together correctly. For integration, design test cases around interface contracts, such as API calls, data formats, error codes and integration points with services. Identify the goal of system testing: to validate the complete system against functional and non functional requirements from the user point of view. For system testing, design test cases as end-to-end scenarios, for example "create order, apply discount, pay, generate invoice" that span many modules and technologies. Compare the options and select the one that clearly distinguishes interface focused integration test cases from business scenario focused system test cases.

Verification / Alternative check:
On real projects, you can see that integration tests often are executed at API or service layer with stubs or mocks for missing parts, while system tests run on a nearly production-like environment with real interfaces and data. Documentation such as technical design specifications drives integration tests, whereas requirement documents and user stories drive system tests. This confirms the difference described in option a.

Why Other Options Are Wrong:
Option b wrongly ties levels of testing to manual versus automated execution; you can automate both integration and system tests.
Option c suggests that only developers or only customers write specific test levels, but in practice both testers and developers collaborate at each level.
Option d ignores the difference in goals and scope, and would lead to redundant or missing tests.

Common Pitfalls:
Teams sometimes jump directly from unit testing to system testing, skipping targeted integration tests. This can make defects harder to localize. Another pitfall is to design system tests that are too technical, focusing on individual APIs rather than user flows. Clear separation of concerns between integration and system test cases leads to more effective testing and easier debugging.

Final Answer:
The main difference is that integration test cases emphasize module interfaces and interactions using technical design, whereas system test cases focus on complete end-to-end business scenarios derived from user and system requirements.