A test system is provided for performing radio-frequency tests on an electronic device under test (DUT) having multiple antennas. The test system may include a test unit for generating radio-frequency test signals, a test enclosure, and a test antenna fixture. The test fixture may include tunable antenna circuitry, antenna tuning elements, a test sensor, a microcontroller, a battery, and a solar cell that charges the battery, each of which is mounted on a test fixture within the test enclosure. The test sensor may be used to detect stimuli issued by the DUT. In response to detecting the stimuli, the microcontroller may send control signals to the antenna tuning elements to configure the antenna circuitry in different modes. Each of the different modes may be optimized to test a selected one of the multiple antennas in the DUT when operating using different radio access technologies and at different frequencies.