Comprehensive and Detailed Explanation From Exact Extract:

Within the SDLC, integration testing is the testing phase that focuses on how different components or modules of the software work together. After individual units or components have been tested in isolation (unit testing), integration testing verifies that the interactions, data flows, and interfaces between these components function correctly as a combined system segment.

Integration testing aims to:

Detect interface defects between modules.

Ensure that combined components communicate and cooperate as intended.

Validate that data passed between modules is correct and handled properly.

Why the other options are incorrect:

B. Unit testing – Focuses on individual components or functions in isolation to verify that each one works correctly on its own, not how they work together.

C. Parallel testing – Involves running the new system and the old system simultaneously to compare outputs, often used during system replacement or migration, not specifically about module interaction.

D. Acceptance testing – Conducted to verify that the system meets business requirements and user needs, typically performed by end users or customers near the end of the SDLC; it is not focused on internal component integration.

Therefore, integration testing is the SDLC testing phase that specifically focuses on how different components of the software work together.