How to test a method in isolation from the rest of the class

module_deep_in_framework.py

class ExampleClass:

    def __init__(self):
        # assume this takes action that you don't want to include in the unit test
        self.something = "data from complicated setup that calls other services"
        print("accessing", self.something)
        

mymodule.py

from module_deep_in_framework import ExampleClass

import external_module

class SubClass(ExampleClass):

    def my_small_method(self):
        if "other services" in self.something:
            # send data
            return external_module.action(
                self.something.split(" ")[0])
        else:
            return external_module.other_action()

test_mymodule.py

from unittest import TestCase, mock

from mymodule import SubClass


class TestMyModule(TestCase):
  
    @mock.patch('mymodule.external_module')
    def test_my_small_method(self, external_module):
        # case: no other services
        doesnt_have_other_services = mock.Mock(something="no services")
        SubClass.my_small_method(doesnt_have_other_services)
        external_module.other_action.assert_called_once_with()
        
        # case: has other services
        has_other_services = mock.Mock(something="data other services")
        SubClass.my_small_method(has_other_services)
        external_module.action.assert_called_with('data')