ch_4_builtin_fixtures

Chapter 4. Builtin Fixtures

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AUT: Cards (To-Do List)

Check all builtin fixtures:

pytest --fixtures

1. List of Builtin Fixtures

1. tmp_path, tmp_path_factory - temp directories
2. capsys - capturing output
3. monkeypatch - changing the env or application code

1.1 tmp_path, tmp_path_factory

Change base directory: pytest --basetemp=<mydir>

1.2 capsys

Related builtin fixtures:

• caplog - capture output written with the logging package
• capdf - capture file descriptors 1 and 2
• capsysbinary - capture bytes
• capfdbinary - capture bytes on file descriptors 1 and 2

1.3 monkeypatch

https://docs.pytest.org/en/7.1.x/how-to/monkeypatch.html

monkeypatch functions:

setattr(target, name, value, raising=True) - sets an attribute delattr(target, name, raising=True) - deletes an attribute setitem(dic, name, value) - sets a dictionary entry delitem(dic, name, raising=True) - deletes a dictionary entry setenv(name, value, prepend=None) - sets an environment variable delenv(name, raising=True) - deletes an environment variable syspath_prepend(path) - prepend path to sys.path (Python's list of import locations) chdir(path) - changes the current working directory

Example of setattr:

# contents of test_app.py, a simple test for our API retrieval
# import requests for the purposes of monkeypatching
import requests

# our app.py that includes the get_json() function
# this is the previous code block example
import app

# custom class to be the mock return value
# will override the requests.Response returned from requests.get
class MockResponse:

    # mock json() method always returns a specific testing dictionary
    @staticmethod
    def json():
        return {"mock_key": "mock_response"}


def test_get_json(monkeypatch):

    # Any arguments may be passed and mock_get() will always return our
    # mocked object, which only has the .json() method.
    def mock_get(*args, **kwargs):
        return MockResponse()

    # apply the monkeypatch for requests.get to mock_get
    monkeypatch.setattr(requests, "get", mock_get)

    # app.get_json, which contains requests.get, uses the monkeypatch
    result = app.get_json("https://fakeurl")
    assert result["mock_key"] == "mock_response"

Fixture:

# contents of test_app.py, a simple test for our API retrieval
import pytest
import requests

# app.py that includes the get_json() function
import app

# custom class to be the mock return value of requests.get()
class MockResponse:
    @staticmethod
    def json():
        return {"mock_key": "mock_response"}


# monkeypatched requests.get moved to a fixture
@pytest.fixture
def mock_response(monkeypatch):
    """Requests.get() mocked to return {'mock_key':'mock_response'}."""

    def mock_get(*args, **kwargs):
        return MockResponse()

    monkeypatch.setattr(requests, "get", mock_get)


# notice our test uses the custom fixture instead of monkeypatch directly
def test_get_json(mock_response):
    result = app.get_json("https://fakeurl")
    assert result["mock_key"] == "mock_response"