TESL addresses the specification of the temporal aspects of an architectural composition language that allows the composition of timed subsystems. TESL specifies the synchronization points between events and time scales. Methodologically, subsystems having potentially different models of execution are abstracted to their interfaces expressed in terms of timed events. In this paper, we present an operational semantics of TESL for constructing symbolic traces that can be used in an online-test scenario: the symbolic trace containing a set of constraints over time-stamps and occurrences of events is matched against concrete runs of the system. We present the operational rules for building symbolic traces and illustrate them with examples. Finally, we show a prototype implementation that generates symbolic traces, and its use for testing.