The invention relates to a test block intended to be implanted in the circuit connecting an apparatus to be tested such as an electricity meter or a protective relay and a power source supplying the apparatus to be tested such as an intensity sensor and/or a voltage sensor. The test block comprises a base including a plurality of inner electric circuits capable of allowing the transmission of information from the power source to the apparatus to be tested and a protective cover intended to be assembled in a dismountable manner with the base in order to form a closed enclosure in which the inner electric circuits are housed. The base and the protective cover are configured such that the removal of the protective cover gives access to a receiving site delimited by the base and capable of receiving by plugging a test plug independent of the test block and electrically linked to a test equipment, in particular a voltmeter and/or an ammeter and/or a dummy current source. A test appliance is also described.