There are things that jump out here to tell me this is a very badly managed compnay
first: you have 2 managers. Any company with any knowledge of decent HR practices and how to minimise stress will never, ever give their employees 2 line managers. It’s the difference between responsibility and accountability. You can have multiple people responsible for giving you work, but only one single set of overarching objectives set by your line manager who is accountable for your performance and ensuring you are treated in accordance to HR policies, the law etc. imho too many organisations do not understand you can have multiple people responsible, but only one person is held accountable. Too often no one is designated as accountable, and people mistake this. That is why you have 2 bosses and why that will always always end in tears
secondly : if they have concerns around who is making mistakes, they certainly can observe you. But to do it as a test, to “catch you out” with people observing in a way that would never be the case irl, is deliberately divisive and starts on premise that they do not trust their employees. Even quite stupid people will realise this. It is not ever going to get the best out of people. It will just make them stressed , and they will not perform the role in the way they normally would. The better way is task shadowing, manager announces there’s some concerns about consistency of results of works, wants to indenting training needs, and the more experienced team member will shadow each of you to both help coach you, but just as importantly to look for systemic failings in their training approach- is the documentation you follow not adequate or clear , do you have an documentation at all, was your instructor led or 1;1 on the job training programme adequate ? During that the “trainer” may pick up on individual issues , or even competency issue which could then be shared with manager, who should them raise it formally in your performance reviews sessions. Asap. Then discuss what you need to support and develop. You do not go around testing people in “surprise” scenario with multiple senior people watching.
to me this is grievance level stuff. It is borderline bullying- but not sure you should use that word and it probably wouldn’t stick in a grievance. I’d base it on that if you did have performance issues, this is not a “fair” test as you were falsely misled into thinking it was a meeting, and then you were being observed in false setting that was going to stress anyone and not reflect what was happening.
but first I would NOW put in writing to ALL those attending, including your other tested colleagues, AND the manager of any HR department that you forewarned your colleagues as you felt this was so unfair and false set up designed explicitly to “catch out” .
Then, on Monday book a meeting with your line manager, or both of them, state you want an explanation as to why they felt this was an appropriate and accurate way to determine who was making the mistakes. Ask them why they had not bought these mistakes to your attention, even if they didn’t know who, immediately and set up time with the more experienced colleague to actually , in a real and non confrontational task shadowing exercise to determine where you were going wrong and fix it. Reiterate that you are new, steep learning curve- if the training wasn’t formalised raise this too . Say clearly, that by setting this unannounced test it has made you stressed (use that word as they have duty of care under HSE to address this, that you feel deeply uncomfortable that they do not trust their staff. Use words “I” all the time , not “you”or “they”. Do not mention your other colleagues. Talk “I feel”, “I felt”, “I was uncomfortable “, “I felt it did not reflect my performance as it placed me under stress and anxiety”, “I am concerned about what the results will be used for “ etc. at end of meeting, send them email with a summary of what you said, they said and any outcomes. Ask them to confirm it’s an accurate reflection. Send a copy to HR if you have HR. KEEP YOUR COPY in case this goes to grievance.
I have worked for 40 years as a manager and senior leader in many companies- never heard of such shite behaviour and ridiculously stupid way to assess perform e or find out where mistakes are made. As someone said earlier, if this is computer work, there should be system to do an audit trail to indenting and gather data to find out who is making mistakes, but more importantly when and why- the when and why is what matters and they should fix first. The who they must regard as incidental until they’ve proved their systems, practices, and policies and training are fit for purpose.