[Python] How to test a form with unique fields using Hypothesis?

I have a model with an unique constrain linking three fields:

class Bookshelf(models.Model):
house = models.CharField(max_length=2, choices=HOUSE_CHOICES, default='Ar')
room = models.CharField(max_length=20, choices=ROOM_CHOICES)
name = models.CharField(max_length=200)
compartments = models.IntegerField(choices=[(x, str(x)) for x in range(1, 9)])
shelves = models.IntegerField(choices=[(x, str(x)) for x in range(1, 9)])

class Meta:
constraints = [
models.UniqueConstraint(fields=['house', 'room', 'name'], name='unique_library')
]

class Book(models.Model):
title = models.CharField(max_length=200)
bookshelf = models.ForeignKey(Bookshelf, on_delete=models.PROTECT, blank=True, null=True)
...


and a modelform to test using hypothesis:

class SearchForm(forms.ModelForm):
class Meta:
model = Book
fields = ['title', 'author_name', 'main_topic', 'subtopic', 'bookshelf', 'vote', 'support']

def __init__(self, *args, **kwargs):
super(SearchForm, self).__init__(*args, **kwargs)
...


My tests often fail with flaky behavior (when I use assume() or exist()) or an IntegrityError. It seems that Hypothesis creates a Bookshelf instance and leaves it in the database between test runs or within the same run. So, when it tries to create a Bookshelf with the same (house, room, name) combination again, it violates the unique constraint. Here same things I try (a little mixed up), I can be more specific about what gives what error:

from hypothesis.strategies import data as hypothesis_data

@composite
def search_form_data(draw):
house = draw(st.text(min_size=1, max_size=10))
room = draw(st.text(min_size=1, max_size=10))
name = draw(st.text(min_size=1, max_size=10))

bookshelf = Bookshelf.objects.create(
house=house,
room=room,
name=name,
compartments=2,
shelves=5
)
# assume(not Bookshelf.objects.filter(house=house, room=room, name=name).exists())
# if not Bookshelf.objects.filter(house=house, room=room, name=name).exists():

return {
'title': draw(st.text(min_size=0, max_size=30)),
'author_name': draw(st.text(min_size=0, max_size=30)),
'bookshelf': bookshelf.id,
}


@given(data=search_form_data())
def test_search_form_accepts_random_valid_input(data):
form = SearchForm(data)
try:
form.is_valid()
except Exception as e:
pytest.fail(f"Unexpected exception: {e}")


@given(
unique_houses=st.sets(st.text(min_size=1, max_size=2), min_size=5, max_size=5),
data=hypothesis_data()
)
def test_search_form_accepts_random_valid_input(unique_houses, data):
for house in unique_houses:
form_data = data.draw(search_form_data(house), label=f"form_data_for_{house}")
form = SearchForm(form_data)

try:
form.is_valid()
except Exception as e:
pytest.fail(f"Unexpected exception: {e}")


@composite
def unique_bookshelf_triplet(draw):
triplet_strategy = st.tuples(
st.text(min_size=1, max_size=3),
st.text(min_size=1, max_size=10),
st.text(min_size=1, max_size=10),
)
seen = draw(st.shared(st.builds(set), key="triplets"))

return draw(
triplet_strategy
.filter(lambda x: x not in seen)
.map(lambda x: seen.add(x) or x)
)

@given(data=hypothesis_data())
def test_create_unique_bookshelves(data):
for _ in range(5):
house, room, name = data.draw(unique_bookshelf_triplet())

bookshelf = Bookshelf.objects.create(
house=house,
room=room,
name=name,
compartments=data.draw(st.integers(min_value=1, max_value=10)),
shelves=data.draw(st.integers(min_value=1, max_value=10)),
)

assert bookshelf.pk is not None


So if I don't check, hypothesis gives many duplicate (integrityerror), If I check the tests become flaky (too many excluded or inconsistent), I tried to generate unique strategies but the results are flaky, probabily I do something very wrong because it's a common situation so it should be easy

Thank you for your help

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