It's really a process of letting the subpoenaed know that they either tell the truth, lie and face perjury charges, or refuse and face contempt or court charges. The latter can seemingly land you in jail in perpetuity. Because fuck you, I guess?
You mean by a court subpoena? If so then you testify or get found in contempt of court.
Or do you mean what if someone is threatened/blackmailed into giving false testimony? If that's the case then you should probably go to the police. If it's law enforcement who are coercing you then I suppose you could try to include that fact in the testimony, but there may not be much difference in that and refusing to comply with the blackmailer in the first place, in terms of your safety.
If you're coerced to lie under oath then I'd guess that still counts as perjury, but I doubt most judges would be mad at you for it; they'd shit fury all over whoever was coercing you.
IDK, imprisoning a person until they either comply or the trial concludes without them seems pretty good for the judge. Bad for the person subpoenaed, but it's no skin of the judge's back
If this happens they'll do the "A person who swears to tell the truth and nothing but the truth says what" ordeal. If that doesn't work they will just let you leave
Generally speaking, you will be asked to swear or affirm that you are going to tell the truth, and that you understand the consequences of not telling the truth. Whether you do a whole ceremony about it or not, it doesn't really matter -- but the court will want to know that you are competent to testify truthfully and that you know that you're not allowed to testify to things you know aren't true.
If you're asking "can you be forced to testify?", the answer is "Yes but it depends." If you're competent to testify and the officers of the court deem your testimony important, they can subpoena your testimony. If you have a reason to contest it, you can -- but "I don't want to" isn't good enough.
I once crossed off something I didn't like on a contract and the boss scolded me and put a fresh new one in front of me while printing out yet another one.
All contracts are negotiable, you did nothing wrong other than not having a conversation before wasting paper, the main issue is that for most people the negotiation is "if you want to work here you have to agree to all this."
But yeah reasonable accommodation and mutual understandings, etc, should be written down and signed. I challenged the non-disclosure agreement at my job once because it literally said I couldn't talk about my work with ANYONE, and a plain reading of it would mean I'd be unable to even talk to my boss about what I was supposed to be doing. It was poorly written and probably unenforceable. My boss didn't like that so I signed it anyway and then focused on finding work elsewhere (he was a dick and his company got raided by the FBI a few years later)