Make CountryTaxBenefitSystem reusable as a fixture

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+### 35.3.5 [#997](https://github.com/openfisca/openfisca-core/pull/997)
+
+#### Technical changes
+
+- In tests, extract `CountryTaxBenefitSystem` to a fixture reusable by all the tests in the test suite.
+  - It allows for a better reusability of test scenarios available to new contributors.
+  - To mitigate possible performance issues, by default the fixture is initialised once per test module.
+
 ### 35.3.4 [#999](https://github.com/openfisca/openfisca-core/pull/999)
 
 #### Technical improvements

README.md

@@ -51,7 +51,7 @@ pytest tests/core/test_parameters.py -k test_parameter_for_period
 
 ## Style
 
-This repository adheres to a certain coding style, and we invite you to follow it for your contributions to be integrated promptly.
+This repository adheres to a [certain coding style](STYLEGUIDE.md), and we invite you to follow it for your contributions to be integrated promptly.
 
 Style checking is already run with `make test`. To run the style checker alone:
 

STYLEGUIDE.md

@@ -0,0 +1,84 @@
+# OpenFisca's Python Style Guide
+
+Arguments over code style and formatting are the bread and butter of most open-source projets out there, including OpenFisca.
+
+To avoid this, we have a style guide, that is a set or arbitrary but consistent conventions about how code should be written, for contributors and maintainers alike.
+
+## Notice
+
+### About this style guide
+
+The present style guide is a work in progress.
+
+It largely follows [Python Foundation's](https://www.python.org/dev/peps/pep-0008/), [NumPy's](https://numpydoc.readthedocs.io/en/latest/format.html) and [Google's](https://google.github.io/styleguide/pyguide.html), but it has a lot of her own as well.
+
+### Contributing
+
+Please refer whenever possible to this style guide both for your contributions and your reviews.
+
+If the style in question is not present and contentious, do not hesitate to include an addition to this guide within your proposal or review.
+
+## Imports
+
+1. In general, use import statements for entire namespaces and modules, rather than for classes and functions. Are exempt of this rule the `typing` module, NumPy's `typing` module, and `openfisca_core` module and submodules (but only in the case of class imports).
+
+2. In general, use absolute import statements rather that relative ones. Are exempt of this rule the modules relative to a submodule of OpenFisca, in order to improve the delimitation of internal and external interfaces.
+
+3. Always follow this order for your imports: system modules, third party modules, third party OpenFisca modules, external OpenFisca Core modules, internal OpenFisca Core modules.
+
+For example given:
+
+```
+/openfisca_core/axes/__init__.py
+/openfisca_core/axes/nothing.py
+/openfisca_core/axes/something.py
+```
+
+Whenever possible we should expect:
+
+```python
+# /openfisca_core/axes/nothing.py
+#
+# Yes
+
+import copy
+from typing import List
+
+import numpy
+from numpy.typing import ArrayLike
+
+from openfisca_country_template import entities
+
+from openfisca_core import tools
+from openfisca_core.variables import Variable
+
+from . import Something
+
+def do(this: List) -> ArrayLike:
+    that = copy.deepcopy(this)
+    array = numpy.ndarray(that)
+    return Something(entities.Person, Variable)
+```
+
+And avoid:
+
+```python
+# /openfisca_core/axes/nothing.py
+#
+# No
+
+from openfisca_country_template.entities import Person
+from openfisca_core import variables
+from openfisca_core.tools import assert_near
+from openfisca_core import axes
+
+from numpy import ndarray
+from copy import deepcopy
+import typing
+import numpy.typing
+
+def do(this: typing.List) -> numpy.typing.ArrayLike:
+    that = deepcopy(this)
+    array = ndarray(that)
+    return axes.Something(Person, variables.Variable)
+```

conftest.py

@@ -0,0 +1,5 @@
+pytest_plugins = [
+    "tests.fixtures.entities",
+    "tests.fixtures.simulations",
+    "tests.fixtures.taxbenefitsystems",
+    ]

setup.py

@@ -1,6 +1,4 @@
 #! /usr/bin/env python
-# -*- coding: utf-8 -*-
-
 
 from setuptools import setup, find_packages
 
@@ -37,7 +35,7 @@
 
 setup(
     name = 'OpenFisca-Core',
-    version = '35.3.4',
+    version = '35.3.5',
     author = 'OpenFisca Team',
     author_email = '[email protected]',
     classifiers = [

tests/core/parameter_validation/test_parameter_clone.py

@@ -1,8 +1,7 @@
-# -*- coding: utf-8 -*-
-from ..test_countries import tax_benefit_system
-
 import os
+
 from openfisca_core.parameters import ParameterNode
+
 BASE_DIR = os.path.dirname(os.path.abspath(__file__))
 year = 2016
 
@@ -20,7 +19,7 @@ def test_clone():
     assert id(clone.node1.param) != id(parameters.node1.param)
 
 
-def test_clone_parameter():
+def test_clone_parameter(tax_benefit_system):
 
     param = tax_benefit_system.parameters.taxes.income_tax_rate
     clone = param.clone()
@@ -32,7 +31,7 @@ def test_clone_parameter():
     assert clone.values_list == param.values_list
 
 
-def test_clone_parameter_node():
+def test_clone_parameter_node(tax_benefit_system):
     node = tax_benefit_system.parameters.taxes
     clone = node.clone()
 
@@ -41,15 +40,15 @@ def test_clone_parameter_node():
     assert clone.children['income_tax_rate'] is not node.children['income_tax_rate']
 
 
-def test_clone_scale():
+def test_clone_scale(tax_benefit_system):
     scale = tax_benefit_system.parameters.taxes.social_security_contribution
     clone = scale.clone()
 
     assert clone.brackets[0] is not scale.brackets[0]
     assert clone.brackets[0].rate is not scale.brackets[0].rate
 
 
-def test_deep_edit():
+def test_deep_edit(tax_benefit_system):
     parameters = tax_benefit_system.parameters
     clone = parameters.clone()