A. During component Integration testing, across any kind of use cases and workflows, especially when integrating different use case features or Integrating with the "backbone" structure of a workflow.

B. During system testing of overall end-to-end behaviors under various load conditions.

C. During acceptance testing, especially for data flows and workflows across key inter-system interfaces. In system integration testing, it is not uncommon for the "user* to be another system or machine (e.g. inputs from sensor inputs and other systems).

D. During unit testing, including using or not profiling information to determine potential bottlenecks and white box techniques to evaluate resource utilization.