Testing class methods with inner third party functions using Pytest in Python

I'm pretty new to pytest. I've built an app and I want to test some of its underlying classes. Suppose one such class looks something like this:

from lib_a import NewInstance

from module_1 import initial_dict

from typing import Optional, Dict


class DataHandler:
    def __init__(self, att1: str) -> None:
        self.cg = NewInstance()
        self.att0 = att0
        self.att1 = att1
        self.prices = Optional[Dict[str, float]] = None
        self.result_dict: Dict[str, float] = {}

    def _get_current_prices(self) -> None:
        raw = self.cg.get_prices(self.att0, self.att1)
        # self.prices = some operation on raw
    
    def calc_answer(self) -> None:
        self._get_current_prices()
        for key, value in initial_dict.items():
            # result_dict[key] = further operations...

Here, lib_a is a pip-installed library that has a class called NewInstance (with one of its methods being get_prices()) that I am using. Basically it is responsible for getting information from the web using requests etc.
In addition, initial_dict is a dictionary that I'm importing from another module.

I did some reading about testing and I have a basic understanding of how to test single functions, but when it comes to classes I am pretty confused as to how to do that exactly. I want to test:

1. The _get_current_prices() method using a mocked .get_prices() response.
2. The calc_answer() method using the result of (1) and a mocked initial_dict.

You can assume that all the # .. operations are some sort of basic math operations on the relevant defined variables.

How does my test file should look to test this class correctly with pytest (I am getting into the habit of using pytest as it is more recommended from what I have read so far).