The test effort required for full test coverage is much higher in event-triggered than in time-triggered real-time systems. Thus, it is hard to attain sufficient confidence in the correctness of event-triggered real-time applications by testing. We present a general upper bound on the test effort of constrained event-triggered real-time systems, assuming multiple resources (a refinement of previous results). The emphasis is on system level testing of application timeliness, assuming that sufficient confidence in its functional correctness has been attained. Covered fault types are mainly incorrect assumptions about temporal attributes. An analysis of our approach shows that designated preemption points are required. A key factor in this approach is the ability to reduce the test effort while maintaining full test coverage.