An embodiment test system is proposed; the test system is used to test electronic devices each one having a case with a plurality of terminals for example, of the BGA type. The test system includes a set of (one or more) test boards. Each test board includes a plurality of banks of electrically conductive receptacles, each one for resting a corresponding electronic device; each receptacle is adapted to receive a terminal of the corresponding electronic device. A set of (one or more) boxes is arranged in operation above the test boards. Each box defines an expandable chamber for a conditioning fluid; particularly, the box includes a rigid body, a flexible membrane of a thermally conductive material facing the test boards, an inlet, and an outlet. Means is provided for controlling a temperature of the conditioning fluid (for example, a heat exchanger). The test system further includes means for forcing the conditioning fluid to circulate under pressure through the chambers, so as to expand the flexible membranes downwardly; the expanded flexible membranes press the electronic devices against the test boards to lock the electronic devices mechanically on the test boards and to condition the electronic devices thermally.