A few things to keep in mind if you have a major test failure:

1. Take a big deep breath and don’t touch anything. Our inclination as engineers is always to poke things and try to fix it right away. That is a bad idea.
2. Leave the room. Go home if its the end of the day. Think, plan, and prepare next steps.
3. Talk with a teammate. Make a list of exactly what you are going to do and what information you hope to gain when you do break configuration of the hardware.
4. Execute that plan to the letter. Take pictures, record, gather all the information you can about the failure because it may not be easy to explain away in the future.

My first major project at JPL was a deployable CubeSat antenna. Before delivering hardware (which did function correctly in orbit!) we had a couple of significant test failures. I would have made my life much easier had I followed the steps above. Remember, slow is steady and steady is fast.