Prerequisite for multiple regression analyses?

Hello everyone,

As part of my master's thesis, I'm conducting a moderated mediation (Hayes Model 7). However, I'm currently checking all the prerequisites for multiple regression analyses. The only thing I'm missing is the "linearity test." Now I have the following problem. My independent variable is a dichotomous variable (values: humorous = 1; not humorous = 2). How do I proceed? I've read several times (although there are no scientific sources) that there's no linearity test for dichotomous independent variables. Is that true? And if so, does anyone know of any scientific sources I could use to support this statement?

Thank you very much for your help in advance.