Electronic device structures may be tested using a radio-frequency test system. The radio-frequency test system may include radio-frequency test equipment and an associated test fixture. The radio-frequency test equipment may be used in generating and measuring radio-frequency signals. The test fixture may contain adjustable structures that allow the positions of radio-frequency test probes to be adjusted. The test system may be configured to position radio-frequency probes in the test fixture so that some probe contacts form electrical connections with conductive antenna structures. The radio-frequency probes may contain other contacts that are positioned to form electrical connections with conductive electronic device housing structures. During radio-frequency testing, the test equipment in the test system may apply radio-frequency test signals to the device structures under test using the test probes. Corresponding radio-frequency test signals may be measured by the test equipment.