147 lines
3.9 KiB
ReStructuredText
147 lines
3.9 KiB
ReStructuredText
=========================
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Parametrize with fixtures
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=========================
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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(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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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 it's 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 and higher 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',
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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`` tells pytest to yield all
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parameters of a fixture.
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.. code-block:: python
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@pytest.fixture(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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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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.. note::
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How should the scoping work in that case? Ideally it uses invocation scope
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and relies on its params
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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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