It's impossible to mock functions when testing class-based components if you utilize ES6 arrow functions.
"Jest can only mock the structure of objects that are present at require time. It does it by reflection (not by analysis), which means that properties that get added by the constructor cannot be mocked. It's important to understand though that a fat-arrow assignment in a class in JS is not a class method; it's a class property holding a reference to a function.
My suggestion to that would be that you change the fat arrow assignments to standard methods and bind them in the constructor. That way they will be Jest aware. Otherwise I'm afraid there's not much we can do here."