Does an expiation for an oath become obligatory for someone who swore not to leave their job until after informing their employer a week in advance, and then broke their oath because the employer did not fulfill their promises, and they left after informing them by only one day?

If your oath was conditional on a man not fulfilling his promise and he did not fulfill it, then there is no expiation (kaffara) upon you, nor is there sin. However, if your oath was not conditional on anything, then expiation for the oath is incumbent upon you, which is feeding ten needy persons, or clothing them, or freeing a slave. If you cannot find any of these, then fasting for three days.