Golang test mock functions best practices

I am developing some tests for my code (using the testing package), and I am wondering what's the best way to mock functions inside the tested function:

Should I pass the function as parameter? In that case, what if that function calls another function? Should I pass both the first and second function as parameters in the tested one?

Note: some of the functions are called on objects (i.e. someObj.Create()) and use HTTP API calls.