Randomizing a user dataclass with pytest and hypothesis


This Content is from Stack Overflow. Question asked by OrenIshShalom

I can manually define an Address builder strategy:

import attrs
from hypothesis import given
import hypothesis.strategies as st

class Address:

    street: str
    city: str

AddressStrategy = st.builds(

def test_proper_address(address):
    assert len(address.city) < 4

When I run pytest, it indeed catches my bug:

address = Address(street='', city='0000') # <--- counterexample address found - good !

    def test_proper_address(address):
>       assert len(address.city) < 4
E       AssertionError: assert 4 < 4
E        +  where 4 = len('0000')
E        +    where '0000' = Address(street='', city='0000').city

main.py:23: AssertionError

According to the docs, it seems like it should be possible to use an auto-generated address builder:

builds() will be used automatically for classes with type annotations on init

But when I try the following options, neither work:

  • st.register_type_strategy(Address)
  • @given(Address)


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