89 lines
2.1 KiB
Markdown
89 lines
2.1 KiB
Markdown
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---
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tags: [python, pytest]
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---
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Fixtures are a way to provide data or state to your tests. Typically, although
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not exclusively, for processes that you want to reuse accross different `test_`
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functions. They are defined at the "arrange" stage of testing.
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## Example: testing class methods under test
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```py
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class Person:
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def __init__(self, name):
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self.name = name
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def print_name(self):
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return f"Your name is {self.name}"
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```
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To create a fixture of this class:
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```py
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@pytest.fixture
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def my_person():
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person = new Person('Thomas')
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return person.name()
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test_print_name(my_person):
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assert(my_person) == 'Thomas'
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```
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> Note we define our fixture and then inject it into our test function.
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> Functions request fixtures they require by declaring them as arguments.
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Alternatively you could just return the class from the fixture and test the
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methods individually within the test function.
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## Integrating with `@patch` to provide mock fixtures
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Say we wanted to mock reading a JSON file.
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We could create a fixture:
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```py
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@pytest fixture
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def raw_json():
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return json.dumps({"key": "value"})
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```
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And pass it in to the mock of the global `open` method:
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```py
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from unittest.mock import mock_open, patch
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def test_json_parsing(raw_json):
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with patch("builtins.open", mock_open(read_data=raw_json))
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# Then assert etc
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```
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This fixture could then be re-used to test any other method that relies on
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incoming JSON from a file.
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## Example: setup and teardown - before each and after each
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Fixtures can be leveraged to setup 'before each...' and 'after each...' logic:
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```py
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@pytest.fixture(scope="function")
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def setup():
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os.environ["POCKET_LAMBDA_ENDPOINT"] = "https://some_endpoint.com/{article_type}"
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yield
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del os.environ["POCKET_LAMBDA_ENDPOINT"]
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```
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Here `yield` is a placeholder for the tests that run in between the setup and
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teardown.
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We use `scope="function"` to signal that this will run before/after any tests
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that inject the fixture.
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Then to specify the units that will run as the `yield` we just inject `setup`:
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```py
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def some_function(setup_function):
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pass
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```
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