The correct selection is C. Automated browser tests depend on the rendered Document Object Model. Salesforce can change internal Lightning markup between seasonal releases even when the business behavior is unchanged, so brittle selectors and DOM assumptions can require test maintenance. From a testing perspective, the goal is deterministic evidence that the solution behaves correctly under the conditions that matter. Tests should isolate external dependencies, use controlled data, exercise positive and negative paths, and reproduce realistic volume or user behavior where required without making production the first place defects are discovered. The alternatives do not provide equivalent evidence: they either validate only a narrow implementation detail or depend on conditions outside the test ' s control. For this scenario, the decisive point is therefore the platform behavior represented by the selected option (C. DOM changes). Applying that rule consistently keeps the implementation aligned with Salesforce-supported lifecycle practices and makes the resulting change easier to review, validate, and operate across environments.

Study Guide reference: Testing — Apex testing; test-data isolation; mocks; regression testing; performance/load testing; sandbox test strategy.