don't mock what you don't own

Jun 21, 2022

https://hynek.me/articles/what-to-mock-in-5-mins/

This article helped me understand the anti-mock viewpoint a bit; in fact it's not actually an anti-mock viewpoint at all, but rather an argument that you should raise the abstraction level to avoid spaghetti mocks.

Basically, he argues that this test, which mocks directly at the HTTP level does not convey intent:

from unittest.mock import Mock
import httpx

def test_empty():
    client = Mock(
        spec_set=httpx.Client,
        get=Mock(
            return_value=Mock(
                spec_set=httpx.Response,
                json=lambda: {
                    "repositories": []
                },
            )
        ),
    )

    assert {} == get_repos_w_tags(client)

While this one, which tests the same thing but adds an abstraction layer above the HTTP request (and therefore mocks what you own rather than the external interface), does:

def test_empty_drc():
    drc = Mock(
        spec_set=DockerRegistryClient,
        get_repos=lambda: []
    )

    assert {} == get_repos_w_tags_drc(drc)
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