dependencies.py

from unittest import mock


# Approach #1 - hidden dependency


def func_1():
    pass


def func_2():
    # You have to read `func_2` code to figure out that it uses `func_1` 👎
    result = func_1()
    ...


def test_func_2():
    # ... and then you have to "patch" it if you want to "unit" test it 😪
    with mock.patch("func_1") as func_1_mock:
        func_1_mock.return_value = ...
        func_2()

    assert ...


# Approach #2 - explicit dependency


class ClassA:
    def method_1(self):
        pass


class ClassB:
    # You can not create `ClassB` instance without providing `ClassA` object 👍
    def __init__(self, class_a: ClassA) -> None:
        self.class_a = class_a

    def method_2(self):
        result = self.class_a.method_1()
        ...


def test_method_1():
    # ... and now test looks beautifull 🎉
    class_a_mock = mock.Mock(spec=ClassA)
    class_a_mock.method_1.return_value = ...
    class_b = ClassB(class_a=class_a_mock)

    class_b.method_2()

    assert ...