Maintenance testing is triggered by changes such as bug fixes, enhancements, or environmental changes.
Option A: "Completion of architecture of the bank system" is not a typical scenario for maintenance testing, as it describes a design phase rather than an operational change.
Option B: "Release of the early draft of the low level project design of an IoT application" is again not suitable for maintenance testing, as it refers to the design phase.
Option C: "Defect was found in a pre-released version of the customer service application" is closer but not quite accurate, as maintenance testing focuses on changes mad (ISTQB not-for-profit association)system is released.
Option D: "Delivery of the hot fix to mobile operating system and ensuring that it still works" is the best example as it directly involves testing after a fix has been implemented.
Therefore, the correct answer is D6†source.
References:
* Certified Tester Foundation Level v4.0
* ISTQB Foundation Level Syllabus 4.0 (2023)