In structured software development and testing, coding starts with unit creation and verification, and integration proceeds layer by layer; this means coding and testing are typically performed in a bottom-up manner (unit to module to subsystem to full system).

Introduction / Context:
Coding and testing activities in the software development life cycle are planned to control risk and localize faults. While design often follows a top-down refinement (from requirements to architecture to detailed design), the act of coding components and verifying them commonly proceeds from the smallest testable pieces upward—i.e., bottom-up. Understanding this distinction helps teams schedule unit tests, integration sequences, and environment readiness in a realistic order.

Given Data / Assumptions:

• Coding produces individual units/classes/functions before full subsystems exist.
• Testing begins with unit tests, then moves to component and integration tests.
• Build pipelines typically assemble tested units into higher-level modules.

Concept / Approach:
Top-down is ideal for analysis and design (decompose big problems). Bottom-up is pragmatic for construction and verification: implement and test leaf modules first, then integrate and test progressively larger aggregates. This minimizes cascading failures and isolates defects early, when they are cheapest to fix.

Step-by-Step Solution:
Identify the development phase: coding plus testing (verification/integration).Note the practical order: create and unit-test low-level components first.Integrate these components into larger modules and test interfaces.Continue upward until the complete system passes system and acceptance tests.

Verification / Alternative check:
In continuous integration pipelines, commits trigger unit tests first; only after passing do builds run higher-level integration suites. This mirrors bottom-up assembly and validation in practice.

Why Other Options Are Wrong:
Ad hoc lacks structure and increases risk. Cross-sectional is not a standard testing progression term. Top-down applies more to design/specification breakdown than to the practical order of coding and verification. “None of the above” is incorrect because bottom-up matches industry practice for build-and-test.

Common Pitfalls:
Confusing design direction with implementation order; assuming top-down always applies. In reality, code is proven reliable from the leaves upward, enabling stable integrations and faster fault localization.

Final Answer:
bottom-up