Circuit breakers for high voltage direct current (HVDC) applications are seen as a required technological step in the development of HVDC grids. The development of several new HVDC circuit breaker prototypes indicate that this step may be achieved in the years to come. In order to facilitate the installation of HVDC circuit breakers, appropriate standards and tests need to be developed. These tests and standards must ensure that the technology is capable of functioning as required. In cases where direct testing cannot be carried out, a synthetic test circuit is used to recreate the conditions of the power system. Testing envelopes which encapsulate the fault currents for two types of voltage source converter under fault conditions are analytically derived in this study and compared with simulations. Testing envelopes allow specifications for HVDC breaker test circuits to be defined. Discussion is also given to the worst type of fault and protection operation time estimates.