A feasibility study of design-for-testability (DFT) of a voltage controlled crystal oscillator with built-in MOS switches to increase its observability and controllability is presented. The primary aim was to assess to what extent the operation of the circuit is changed when the switches are introduced. The possibility of non-destructive localization of faulty components in the provided test modes and the temperature/frequency characteristics measurements are briefly described. Finally, on the basis of the presented experimental work, a design-for-test procedure for crystal oscillator circuits is summarized. The work was performed in a development phase of a voltage controlled temperature compensated crystal oscillator.