I have had a faulty socket, but that is rare. The main reason for a socket to fail, is the 3.5 mm screws have hit a wire when screwing the socket into the box.
Working on electrics, one must test what one has done, but these



are not cheap, likely cost me around £150 to get the test gear, and for most people cheaper to get an electrician to do the work than hire or buy the test gear. I admit I don't always test as I should, but if something goes wrong, then one has to get the testers out.
Likely most faults can be found using the multi-meter

here seen testing the earth leakage, but same meter has non-contact volts test, volts measured with leads, ohms measured with leads, and AC and DC amps with the jaws, so my total earth leakage is 8 mA as shown with the meter. That meter cost me £35. As did the insulation tester, the RCD tester was around £90, so what have you got to test with?