Your question boils down to whether or not the quantum circuit that entangles the qubits works correctly. You can simply test the reliability of the quantum circuit by running it multiple times and checking that the outcomes behave as you expect. For example, if your circuit is supposed to generate the entagled pair [00 or 11 with equal probability] you would expect measurements to either be 00 or 11 and never 01 or 10.

The act of measurement on the second particle destroys the entagled state of the pair. That effect can be measured on the first particle's side (which may be far away... on the other side of the galaxy maybe).