Rewrite unit tests migrated from doctests

[Michal Petrucha]

There's quite a lot of unit tests that have been rewritten 1:1 from doctests. These tests tend to verify all aspects of a certain feature at once, they modify the state of the database throughout the whole test and by the end of the test no one really knows what the database state is supposed to be.

For example, modeltests.generic_relations.GenericRelationsTests.test_generic_relations walks through most of the features supported by GenericForeignKeys, it is 130 lines long and in case the last assertion fails, you'll have to spend ridiculous amounts of time figuring out what happened.

A likely incomplete list of similar tests:
modeltests.basic.ModelTest.test_lookup
modeltests.basic.ModelTest.test_object_creation
modeltests.custom_columns.CustomColumnsTests.test_db_column
modeltests.custom_managers.CustomManagerTests.test_manager
modeltests.custom_pk.CustomPKTests.test_custom_pk
modeltests.defer.DeferTests.test_defer
modeltests.expressions.ExpressionsTests.test_filter
modeltests.field_subclassing.CustomField.test_custom_field
modeltests.files.FileStorageTests.test_files
modeltests.get_or_create.GetOrCreateTests.test_get_or_create
modeltests.m2m_recursive.RecursiveM2MTests.test_recursive_m2m
modeltests.m2m_signals.ManyToManySignalsTest
modeltests.m2m_through.M2mThroughTests
modeltests.model_formsets.ModelFormsetTests
modeltests.model_forms.OldFormForXTests.test_with_data (This one has more than 500 lines!)
modeltests.model_inheritance.ModelInheritanceTests
modeltests.model_package.ModelPackageTests.test_model_packages
modeltests.order_with_respect_to.OrderWithRespectToTests.test_basic
modeltests.signals.SignalTests.test_basic

I only went through modeltests/*/tests.py; I might have overlooked a few tests.

This ticket is meant to track all of them; each time a test is updated, we can strike it out in the list above and once there is no item left, we can close this. The point is to make the test suite help developers as much as possible.

[Mark Smith]

Last attempt to get the status of this ticket correct.

[Mark Smith]

Basic test refactorings now committed at ​https://github.com/bedmondmark/django/tree/test_refactor - I'll issue a Pull Request when I've finished the whole lot.

[Michal Petrucha]

Found another candidate: regressiontests.defer_regress.DeferRegressionTest.test_basic

IMO, this test is broken because its results depend on the order of execution of tests as it accesses the global model class storage. This means it won't be that easy to rewrite this test.

[modi.konark@…]

Tried Merging the pull request by koniiik, there were lot of conflicts. The test directory layout has changed and also the conventions used needed to be re-worked.

Will be re-writing the tests and issue a pull request as and when they are done.

​https://github.com/django/django/pull/923 , for the test " Custom Columns " .

[Claude Paroz]

I'd just like to note that cutting single tests in multiple tests has a cost for the test suite, as the database is flushed between tests. So it's right and fine to separate tests when testing different features, but don't just create test methods for each single database request.

[Carl Meyer <carl@…>]

In 483e1b807e7a3c9e49fe5fcbf9b1300ef98a381c:

Refs #18586 -- Split out long custom_columns lookup test into multiple tests.