Add decorators for skipping tests when run without indicated Django s…

…upport.

Many unit tests can only be run if the version of Django includes
certain support. For instance, migration-related unit tests require
support for migrations in Django. Previously, every such unit test had
to have its own checks and handle raising a `SkipTest`, but this was
getting tedious to maintain, and isn't very future-proof.

This change adds some new decorators for these tests, and standardizes
the `SkipTest` message. This simplifies much of the code and improves
maintainability going forward.

Testing Done:
All unit tests pass across all versions of Django.

Verified that the skip message output was correct in older versions.

Reviewed at https://reviews.reviewboard.org/r/11248/

django_evolution/tests/decorators.py

@@ -0,0 +1,122 @@
+"""Decorators to aid in creating unit tests.
+
+Version Added:
+    2.1
+"""
+
+from __future__ import unicode_literals
+
+from functools import wraps
+from unittest import SkipTest
+
+import django
+
+from django_evolution.support import (supports_constraints,
+                                      supports_index_together,
+                                      supports_indexes,
+                                      supports_migrations)
+
+
+def _build_requires_support_decorator(flag, skip_message):
+    """Build a decorator checking for Django support for a feature.
+
+    Args:
+        flag (bool):
+            The support flag to check.
+
+        skip_message (unicode):
+            The skip message. This should have ``%(django_version)s`` in the
+            message somewhere.
+
+    Raises:
+        unittest.SkipTest:
+            Raised if run on a version of Django without the required support.
+    """
+    def _decorator(func):
+        @wraps(func)
+        def _wrapper(*args, **kwargs):
+            if not flag:
+                raise SkipTest(skip_message % {
+                    'django_version': '%s.%s' % django.VERSION[:2],
+                })
+
+            return func(*args, **kwargs)
+
+        return _wrapper
+
+    return _decorator
+
+
+#: Decorator to require Meta.constraints support for running a test.
+#:
+#: Args:
+#:     func (callable):
+#:         The unit test function to wrap.
+#:
+#: Raises:
+#:     unittest.SkipTest:
+#:         The current version of Django doesn't support ``Meta.constraints``.
+requires_meta_constraints = _build_requires_support_decorator(
+    flag=supports_constraints,
+    skip_message=("Meta.constraints isn't supported on Django "
+                  "%(django_version)s"))
+
+
+#: Decorator to require Meta.index_together support for running a test.
+#:
+#: Args:
+#:     func (callable):
+#:         The unit test function to wrap.
+#:
+#: Raises:
+#:     unittest.SkipTest:
+#:         The current version of Django doesn't support
+#:         ``Meta.index_together``.
+requires_meta_index_together = _build_requires_support_decorator(
+    flag=supports_index_together,
+    skip_message=("Meta.index_together isn't supported on Django "
+                  "%(django_version)s"))
+
+
+#: Decorator to require Meta.indexes support for running a test.
+#:
+#: Args:
+#:     func (callable):
+#:         The unit test function to wrap.
+#:
+#: Raises:
+#:     unittest.SkipTest:
+#:         The current version of Django doesn't support ``Meta.indexes``.
+requires_meta_indexes = _build_requires_support_decorator(
+    flag=supports_indexes,
+    skip_message="Meta.indexes isn't supported on Django %(django_version)s")
+
+
+#: Decorator to require migrations support for running a test.
+#:
+#: Args:
+#:     func (callable):
+#:         The unit test function to wrap.
+#:
+#: Raises:
+#:     unittest.SkipTest:
+#:         The current version of Django doesn't support migrations.
+requires_migrations = _build_requires_support_decorator(
+    flag=supports_migrations,
+    skip_message="Migrations aren't supported on Django %(django_version)s")
+
+
+#: Decorator to require migration history checks for running a test.
+#:
+#: Args:
+#:     func (callable):
+#:         The unit test function to wrap.
+#:
+#: Raises:
+#:     unittest.SkipTest:
+#:         The current version of Django doesn't support performing history
+#:         checks when running migrations.
+requires_migration_history_checks = _build_requires_support_decorator(
+    flag=(django.VERSION >= (1, 10)),
+    skip_message=("Migration history checks aren't supported on Django "
+                  "%(django_version)s"))

django_evolution/tests/test_change_meta.py

@@ -4,7 +4,6 @@
 
 from django.db import models
 from django.db.models import Q
-from nose import SkipTest
 
 try:
     # Django >= 2.2
@@ -23,9 +22,11 @@
 
 from django_evolution.mutations import ChangeMeta
 from django_evolution.support import (supports_constraints,
-                                      supports_indexes,
-                                      supports_index_together)
+                                      supports_indexes)
 from django_evolution.tests.base_test_case import EvolutionTestCase
+from django_evolution.tests.decorators import (requires_meta_constraints,
+                                               requires_meta_index_together,
+                                               requires_meta_indexes)
 from django_evolution.tests.models import BaseTestModel
 
 
@@ -111,13 +112,10 @@ class ChangeMetaConstraintsTests(EvolutionTestCase):
     )
 
     @classmethod
+    @requires_meta_constraints
     def setUpClass(cls):
         super(ChangeMetaConstraintsTests, cls).setUpClass()
 
-        if not supports_constraints:
-            raise SkipTest('Meta.constraints is not supported on this version '
-                           'of Django')
-
     def test_keeping_empty(self):
         """Testing ChangeMeta(constraints) and keeping list empty"""
         class DestModel(BaseTestModel):
@@ -372,13 +370,10 @@ class ChangeMetaIndexesTests(EvolutionTestCase):
     )
 
     @classmethod
+    @requires_meta_indexes
     def setUpClass(cls):
         super(ChangeMetaIndexesTests, cls).setUpClass()
 
-        if not supports_indexes:
-            raise SkipTest('Meta.indexes is not supported on this version '
-                           'of Django')
-
     def test_keeping_empty(self):
         """Testing ChangeMeta(indexes) and keeping list empty"""
         class DestModel(BaseTestModel):
@@ -580,13 +575,10 @@ class ChangeMetaIndexTogetherTests(EvolutionTestCase):
     )
 
     @classmethod
+    @requires_meta_index_together
     def setUpClass(cls):
         super(ChangeMetaIndexTogetherTests, cls).setUpClass()
 
-        if not supports_index_together:
-            raise SkipTest('Meta.index_together is not supported on this '
-                           'version of Django')
-
     def test_keeping_empty(self):
         """Testing ChangeMeta(index_together) and keeping list empty"""
         class DestModel(BaseTestModel):

django_evolution/tests/test_evolution_graph.py

@@ -2,15 +2,14 @@
 
 from __future__ import unicode_literals
 
-from unittest import SkipTest
-
 from django.db import DEFAULT_DB_ALIAS, connections
 
 from django_evolution.compat.apps import get_app
 from django_evolution.models import Evolution, Version
 from django_evolution.support import supports_migrations
 from django_evolution.tests.base_test_case import (MigrationsTestsMixin,
                                                    TestCase)
+from django_evolution.tests.decorators import requires_migrations
 from django_evolution.tests.evolutions_app.models import EvolutionsAppTestModel
 from django_evolution.tests.evolutions_app2.models import \
     EvolutionsApp2TestModel
@@ -153,11 +152,9 @@ def test_add_evolutions(self):
                 'app': app,
             })
 
+    @requires_migrations
     def test_add_migration_plan(self):
         """Testing EvolutionGraph.add_migration_plan"""
-        if not supports_migrations:
-            raise SkipTest('Not used on Django < 1.7')
-
         class TestsInitialMigration(migrations.Migration):
             pass
 
@@ -290,11 +287,9 @@ def test_mark_evolutions_applied(self):
                 'app': app,
             })
 
+    @requires_migrations
     def test_mark_migrations_applied(self):
         """Testing EvolutionGraph.mark_migrations_applied"""
-        if not supports_migrations:
-            raise SkipTest('Not used on Django < 1.7')
-
         class TestsInitialMigration(migrations.Migration):
             pass
 

django_evolution/tests/test_evolver.py

@@ -11,8 +11,6 @@
     # Django < 1.7
     migrations = None
 
-from nose import SkipTest
-
 from django_evolution.compat.apps import (get_app,
                                           get_apps,
                                           register_app_models)
@@ -33,7 +31,6 @@
                                       created_models,
                                       creating_models)
 from django_evolution.signature import AppSignature, ModelSignature
-from django_evolution.support import supports_migrations
 from django_evolution.tests import models as evo_test
 from django_evolution.tests.evolutions_app import models as test_app2
 from django_evolution.tests.base_test_case import (EvolutionTestCase,
@@ -43,6 +40,7 @@
                                           execute_test_sql,
                                           register_models)
 from django_evolution.utils.apps import get_app_label
+from django_evolution.tests.decorators import requires_migrations
 from django_evolution.utils.migrations import (MigrationList,
                                                record_applied_migrations)
 
@@ -611,13 +609,11 @@ def tearDown(self):
         creating_models.disconnect(self._on_creating_models)
         created_models.disconnect(self._on_created_models)
 
+    @requires_migrations
     def test_prepare_tasks_with_migrations_new_app(self):
         """Testing EvolveAppTask.prepare_tasks with migrations for new
         app
         """
-        if not supports_migrations:
-            raise SkipTest('Not used on Django < 1.7')
-
         class MigrationTestModel(BaseTestModel):
             field1 = models.IntegerField()
             field3 = models.BooleanField()
@@ -703,13 +699,11 @@ class RemoveFieldMigration(migrations.Migration):
                 ('tests', '0003_remove_field'),
             ])
 
+    @requires_migrations
     def test_prepare_tasks_with_migrations_some_applied(self):
         """Testing EvolveAppTask.prepare_tasks with migrations and some
         already applied
         """
-        if not supports_migrations:
-            raise SkipTest('Not used on Django < 1.7')
-
         class MigrationTestModel(BaseTestModel):
             field1 = models.IntegerField()
             field3 = models.BooleanField()
@@ -794,11 +788,9 @@ class RemoveFieldMigration(migrations.Migration):
                 ('tests', '0003_remove_field'),
             ])
 
+    @requires_migrations
     def test_execute_tasks_with_migrations(self):
         """Testing EvolveAppTask.execute_tasks with migrations"""
-        if not supports_migrations:
-            raise SkipTest('Not used on Django < 1.7')
-
         class MigrationTestModel(BaseTestModel):
             field1 = models.IntegerField()
             field2 = models.CharField(max_length=10)
@@ -895,12 +887,10 @@ class AddFieldMigration(migrations.Migration):
                                               field2='foo',
                                               field3=True)
 
+    @requires_migrations
     def test_execute_tasks_with_evolutions_and_migrations(self):
         """Testing EvolveAppTask.execute_tasks with evolutions and migrations
         """
-        if not supports_migrations:
-            raise SkipTest('Not used on Django < 1.7')
-
         class EvolveMigrateTestModel(BaseTestModel):
             field1 = models.IntegerField()