Modular verification in VHDL design: After each sub-circuit within a VHDL subsection has been individually validated, what should be done before integrating and testing the subsection as a whole?

Introduction / Context:
Complex digital systems are built from smaller components. A sound VHDL workflow emphasizes modularity: design small units, verify them, then integrate. Knowing the proper sequence reduces debug time and prevents fault propagation to higher hierarchy levels.

Given Data / Assumptions:

• Sub-circuits (entities/architectures) exist within a subsection.
• Goal is to integrate these units into a larger block.
• Validation means functional simulation (and optionally formal checks) before integration.

Concept / Approach:
Unit testing (component-level verification) confirms each block meets its specification in isolation, using focused testbenches. Only after passing these tests does it make sense to combine components, otherwise integration testing becomes murky with multiple unknown failure sources.

Step-by-Step Solution:

Verification / Alternative check:
Adopt continuous integration practices: run regression test suites after every change; ensure unit tests pass before system-level simulation and synthesis.

Why Other Options Are Wrong:

Common Pitfalls:
Skipping unit tests and relying only on top-level checks; inadequate test coverage; not stubbing external interfaces, making unit tests brittle.

Final Answer:
tested