A test fixture for testing microstrip assemblies and similar electronic circuit components and assemblies under application of high-frequency signals introduced through launchers whose positions are adjustable in the test fixture to accommodate circuit assemblies of different sizes and different geometry. An easily operated rapid connector positioning mechanism moves connectors which complete electrical connection between outer conductors of the launchers and a ground plane conductor of a microstrip assembly. The connectors also lift the microstrip assembly and support it while electrical connection is completed, without the need for a carrier beneath the test assembly. A lid is moved in coordination with operation of the connector positioning mechanism to provide electrical contact to a third point on the upper face of a circuit assembly to be tested.