Mock static functions called in the main function that is being tested

I want to mock some functions within a function, I am testing. I have a class that has several static private functions being called from one so-called mainFunction. I want to particularly test the result of MyClass.functionD (called by mainFunction) which is a private method, therefore, I would like to mock MyClass.fucntionA, MyClass.fucntionB and MyClass.fucntionA to return a default result so that my test can focus on the result of MyClass.fucntionD.

export default class MyClass {       static mainFunction(paramA: string, paramB: number): boolean {            if (MyClass.fucntionA(paramA, paramB)) {              return false;          }            if (!MyClass.fucntionB(paramA, paramB)) {              return false;          }            if (MyClass.fucntionC(paramA, paramB)) {              return false;          }            // I need to focus on the result of this function (i.e. private) for my test          if (MyClass.fucntionD(paramA)) {              return false;          }            return true;     }    }  

So far, I have tried jest spyOn and some default mock function but I am just lost and cannot proceed as I am really new to typescript / Javascript. Any hint/reference related to how I should proceed would be enough for me. :) Thanks.

from Recent Questions - Stack Overflow https://stackoverflow.com/questions/65376946/mock-static-functions-called-in-the-main-function-that-is-being-tested Intesar Haider