pytest-mock 模拟自我方法

Question

I'm trying to mock a self method using pytest-mock.

Simply my class got a function "distance" which I want to mock.

I want to test my eq function that is like this:

def __eq__(self, other):
        return self.distance() == other.distance()

I try something like this:

def test_eq(mocker):
    i = mocker.MagicMock(Interval)
    mocker.patch.object(i, 'distance', return_value=1)
    i2 = mocker.MagicMock(Interval)
    mocker.patch.object(i2, 'distance', return_value=1)

    assert i == i2

But this return:

AssertionError: assert <\\MagicMock spec='Interval' id='140333310434384'> ==<\\MagicMock spec='Interval' id='140333310558104'>

I have also tried

mocker.patch.object(i, 'self.distance', return_value=1)

but this get me an AttributeError as i expected from MagicMock.

What is the right way to patch my object self method?

Answer 1

I don't think you can patch 'Interval' like this. Instead you should patch the constructor and manually replace the distance functions to return expected results.

This example will only test the Interval.__eq__ method:

def test_eq(mocker):
    # Mock constructor as it is already tested elsewhere
    mocker.patch.object(Interval, "__init__", return_value=None)

    i1 = Interval()
    i1.distance = lambda: 1

    i2 = Interval()
    i2.distance = lambda: 1

    assert i1 == i2

Answer 2

You can easily mock out the distance method like this. Assuming that your Interval class is defined in the interval module for example like this:

class Interval:
    def __eq__(self, other):
        return self.distance() == other.distance()

    def distance(self):
        raise NotImplementedError()

Then in your test you can just mock out the distance function to always return 1 like this:

from interval import Interval

def test_eq(mocker):
    mocker.patch('interval.Interval.distance', return_value=1)

    i1 = Interval()
    i2 = Interval()

    assert i1 == i2