165 lines
4.2 KiB
ReStructuredText
165 lines
4.2 KiB
ReStructuredText
:orphan:
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===================================
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PROPOSAL: Parametrize with fixtures
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===================================
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.. warning::
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This document outlines a proposal around using fixtures as input
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of parametrized tests or fixtures.
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Problem
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-------
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As a user I have functional tests that I would like to run against various
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scenarios.
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In this particular example we want to generate a new project based on a
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cookiecutter template. We want to test default values but also data that
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emulates user input.
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- use default values
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- emulate user input
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- specify 'author'
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- specify 'project_slug'
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- specify 'author' and 'project_slug'
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This is how a functional test could look like:
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.. code-block:: python
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import pytest
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@pytest.fixture
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def default_context():
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return {"extra_context": {}}
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@pytest.fixture(
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params=[
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{"author": "alice"},
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{"project_slug": "helloworld"},
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{"author": "bob", "project_slug": "foobar"},
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]
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)
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def extra_context(request):
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return {"extra_context": request.param}
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@pytest.fixture(params=["default", "extra"])
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def context(request):
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if request.param == "default":
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return request.getfuncargvalue("default_context")
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else:
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return request.getfuncargvalue("extra_context")
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def test_generate_project(cookies, context):
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"""Call the cookiecutter API to generate a new project from a
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template.
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"""
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result = cookies.bake(extra_context=context)
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assert result.exit_code == 0
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assert result.exception is None
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assert result.project.isdir()
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Issues
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------
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* By using ``request.getfuncargvalue()`` we rely on actual fixture function
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execution to know what fixtures are involved, due to its dynamic nature
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* More importantly, ``request.getfuncargvalue()`` cannot be combined with
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parametrized fixtures, such as ``extra_context``
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* This is very inconvenient if you wish to extend an existing test suite by
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certain parameters for fixtures that are already used by tests
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pytest version 3.0 reports an error if you try to run above code::
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Failed: The requested fixture has no parameter defined for the current
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test.
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Requested fixture 'extra_context'
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Proposed solution
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-----------------
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A new function that can be used in modules can be used to dynamically define
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fixtures from existing ones.
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.. code-block:: python
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pytest.define_combined_fixture(
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name="context", fixtures=["default_context", "extra_context"]
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)
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The new fixture ``context`` inherits the scope from the used fixtures and yield
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the following values.
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- ``{}``
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- ``{'author': 'alice'}``
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- ``{'project_slug': 'helloworld'}``
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- ``{'author': 'bob', 'project_slug': 'foobar'}``
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Alternative approach
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--------------------
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A new helper function named ``fixture_request`` would tell pytest to yield
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all parameters marked as a fixture.
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.. note::
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The `pytest-lazy-fixture <https://pypi.org/project/pytest-lazy-fixture/>`_ plugin implements a very
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similar solution to the proposal below, make sure to check it out.
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.. code-block:: python
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@pytest.fixture(
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params=[
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pytest.fixture_request("default_context"),
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pytest.fixture_request("extra_context"),
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]
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)
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def context(request):
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"""Returns all values for ``default_context``, one-by-one before it
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does the same for ``extra_context``.
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request.param:
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- {}
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- {'author': 'alice'}
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- {'project_slug': 'helloworld'}
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- {'author': 'bob', 'project_slug': 'foobar'}
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"""
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return request.param
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The same helper can be used in combination with ``pytest.mark.parametrize``.
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.. code-block:: python
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@pytest.mark.parametrize(
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"context, expected_response_code",
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[
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(pytest.fixture_request("default_context"), 0),
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(pytest.fixture_request("extra_context"), 0),
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],
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)
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def test_generate_project(cookies, context, exit_code):
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"""Call the cookiecutter API to generate a new project from a
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template.
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"""
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result = cookies.bake(extra_context=context)
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assert result.exit_code == exit_code
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