Before revision: For Level A/B, test coverage analysis should confirm that all nodes and interconnections have been exercised (comparable to DO-178C structural coverage objectives), while for Level C it is only needed to demonstrate correct operation under all combinations and permutations of conditions of applied only to the inputs of the device (black box), and Level D testing can be accomplished through indirect tests applied to the system that has the item installed.
After revision: For Level A/B, test coverage analysis should confirm that all nodes and interconnections have been exercised (comparable to DO-178C structural coverage objectives), while for Level C it is only needed to demonstrate correct operation under all combinations and permutations conditions of applied only to the inputs of the device (black box), and Level D testing can be accomplished through indirect tests applied to the system that has the item installed.