Although untimed system testing has already been far studied, its timed counterpart is still a rather new field and few methodologies have been proposed so far. This paper develops a method for testing timed systems through the generation of test purposes from the specification, modeled as a timed input/output automaton (TIOA), i.e. an automaton where each transition is labeled with time constraints in addition to the usual input or output symbol. This automaton is first translated into a semantically equivalent LTS (Labeled Transition System) from which we derive both the timed test purposes and their canonical tester. The test sequences are then executed on the implementation through a dedicated test architecture. This execution allows both to discriminate between the different cases (input, output or waiting) and to test a representative part of the infinite set of clock values.