django test - how to avoid the ForeignKeyViolation

Question

I am struggling to create tests with django with objects that have foreign keys. The tests run with no errors when run individually, but when running all, i get ForeignKeyViolation in the teardown phase (which I don't understand what it does and can't find any info on it).

When starting the testsuite I am creating a bunch of dummy data like this:

def setUp(self) -> None:
    create_bulk_users(5)
    create_categories()
    create_tags()
    create_technologies()
    self.tags = Tag.objects.all()
    self.categories = Category.objects.all()
    self.technologies = Technology.objects.all()

The problems I need help figuring out are:

1. What exactly the teardown phase does? Are there any detailed docs on it?
2. How should I structure my tests so to avoid the ForeignKeyViolation issue?

Answer 1

What exactly the teardown phase does? Are there any detailed docs on it?

I couldn't find any detailed docs about it. All I find out was by reading the actual code. Teardown cancels any operations done to the DB during the tests.

The way TestCases work (broadly) is this:

1. SetUp method runs **before** every test
2. individual test method is run
3. TearDown method runs **after** every test
4. Test database is flushed

How should I structure my tests so to avoid the ForeignKeyViolation issue?

My mistake was that I was importing a function for creating dummy data. The imported module was running a function to populate some primary data. The problem was that was not rerun each within the setUp method because it would run just one, when importing the file.

# imported module

# will delete all tags after running first test but
# the reference to the old tags will persist

tags = FakeTags.create_bulk();

def create_bulk_articles():
    article = FakeArticle.create()
    article.tags.add(tags)

I fixed it by just using the trouble function inside the imported function.

# imported module

# tags are created each time before running the tests

def create_bulk_articles():
    tags = FakeTags.create_bulk();
    article = FakeArticle.create()
    article.tags.add(tags)