What decisions were made? Why? What are the advantages and disadvantages of this particular test plan?

Given the following subsystem decomposition:








comment on the testing plan used by the project manager:

This test plan was generated according to a sandwich testing plan, without unit testing subsystems from the target
layer and without double tests. The advantage is that this test plan consists of fewer tasks. The disadvantage is that
failures discovered during the Test A,B,C,D activity will be difficult to locate. A better strategy is to unit test the
subsystems in the target layer.