Improve Hypothesis test robustness (#684)

* Improve Hypothesis test robustness

* Add tests for `test_assert_only_unstructured_passes_for_primitives`

Author: Tinche

HISTORY.md

@@ -11,6 +11,13 @@ The third number is for emergencies when we need to start branches for older rel
 
 Our backwards-compatibility policy can be found [here](https://github.com/python-attrs/cattrs/blob/main/.github/SECURITY.md).
 
+## NEXT (UNRELEASED)
+
+- Fix unstructuring NewTypes with the {class}`BaseConverter`.
+  ([#684](https://github.com/python-attrs/cattrs/pull/684))
+- Make some Hypothesis tests more robust.
+  ([#684](https://github.com/python-attrs/cattrs/pull/684))
+
 ## 25.2.0 (2025-08-31)
 
 - **Potentially breaking**: Sequences are now structured into tuples.

src/cattrs/converters.py

@@ -227,6 +227,10 @@ def __init__(
         )
         self._unstructure_func.register_func_list(
             [
+                (
+                    lambda t: get_newtype_base(t) is not None,
+                    lambda o: self.unstructure(o, unstructure_as=o.__class__),
+                ),
                 (
                     is_protocol,
                     lambda o: self.unstructure(o, unstructure_as=o.__class__),

tests/helpers.py

@@ -0,0 +1,20 @@
+"""Helpers for tests."""
+
+from typing import Any
+
+
+def assert_only_unstructured(obj: Any):
+    """Assert the object is comprised of only unstructured data:
+
+    * dicts, lists, tuples
+    * strings, ints, floats, bools, None
+    """
+    if isinstance(obj, dict):
+        for k, v in obj.items():
+            assert_only_unstructured(k)
+            assert_only_unstructured(v)
+    elif isinstance(obj, (list, tuple, frozenset, set)):
+        for e in obj:
+            assert_only_unstructured(e)
+    else:
+        assert isinstance(obj, (int, float, str, bool, type(None)))

tests/test_converter.py

@@ -32,6 +32,7 @@
 from cattrs.gen import make_dict_structure_fn, override
 
 from ._compat import is_py310_plus
+from .helpers import assert_only_unstructured
 from .typed import (
     nested_typed_classes,
     simple_typed_attrs,
@@ -54,7 +55,7 @@ def test_simple_roundtrip(cls_and_vals, detailed_validation):
     cl, vals, kwargs = cls_and_vals
     inst = cl(*vals, **kwargs)
     unstructured = converter.unstructure(inst)
-    assert "Hyp" not in repr(unstructured)
+    assert_only_unstructured(unstructured)
     assert inst == converter.structure(unstructured, cl)
 
 
@@ -73,7 +74,7 @@ def test_simple_roundtrip_tuple(cls_and_vals, dv: bool):
     cl, vals, _ = cls_and_vals
     inst = cl(*vals)
     unstructured = converter.unstructure(inst)
-    assert "Hyp" not in repr(unstructured)
+    assert_only_unstructured(unstructured)
     assert inst == converter.structure(unstructured, cl)
 
 
@@ -125,7 +126,7 @@ def test_simple_roundtrip_with_extra_keys_forbidden(cls_and_vals, strat):
     assume(strat is UnstructureStrategy.AS_DICT or not kwargs)
     inst = cl(*vals, **kwargs)
     unstructured = converter.unstructure(inst)
-    assert "Hyp" not in repr(unstructured)
+    assert_only_unstructured(unstructured)
     assert inst == converter.structure(unstructured, cl)
 
 

tests/test_gen_dict.py

@@ -13,6 +13,7 @@
 from cattrs.errors import ClassValidationError, ForbiddenExtraKeysError
 from cattrs.gen import make_dict_structure_fn, make_dict_unstructure_fn, override
 
+from .helpers import assert_only_unstructured
 from .typed import nested_typed_classes, simple_typed_classes, simple_typed_dataclasses
 from .untyped import nested_classes, simple_classes
 
@@ -143,8 +144,7 @@ def test_individual_overrides(converter_cls, cl_and_vals):
     inst = cl(*vals, **kwargs)
 
     res = converter.unstructure(inst)
-    assert "Hyp" not in repr(res)
-    assert "Factory" not in repr(res)
+    assert_only_unstructured(res)
 
     for attr, val in zip(fields, vals):
         if attr.name == chosen_name:
@@ -181,7 +181,7 @@ def test_unmodified_generated_structuring(cl_and_vals, dv: bool):
 
     unstructured = converter.unstructure(inst)
 
-    assert "Hyp" not in repr(unstructured)
+    assert_only_unstructured(unstructured)
 
     converter.register_structure_hook(cl, fn)
 

tests/test_helpers.py

@@ -0,0 +1,52 @@
+"""Tests for test helpers."""
+
+import pytest
+from attrs import define
+
+from .helpers import assert_only_unstructured
+
+
+def test_assert_only_unstructured_passes_for_primitives():
+    """assert_only_unstructured should pass for basic Python data types."""
+    # Test primitives
+    assert_only_unstructured(42)
+    assert_only_unstructured("hello")
+    assert_only_unstructured(3.14)
+    assert_only_unstructured(True)
+    assert_only_unstructured(None)
+
+    # Test collections of primitives
+    assert_only_unstructured([1, 2, 3])
+    assert_only_unstructured({"key": "value", "number": 42})
+    assert_only_unstructured((1, "two", 3.0))
+    assert_only_unstructured({1, 2, 3})
+    assert_only_unstructured(frozenset([1, 2, 3]))
+
+    # Test nested structures
+    assert_only_unstructured(
+        {"list": [1, 2, {"nested": "dict"}], "tuple": (True, None), "number": 42}
+    )
+
+
+def test_assert_only_unstructured_fails_for_attrs_classes():
+    """assert_only_unstructured should fail for attrs classes."""
+
+    @define
+    class SimpleAttrsClass:
+        value: int
+
+    instance = SimpleAttrsClass(42)
+
+    # Should raise AssertionError for attrs class instance
+    with pytest.raises(AssertionError):
+        assert_only_unstructured(instance)
+
+    # Should also fail when attrs instance is nested in collections
+    with pytest.raises(AssertionError):
+        assert_only_unstructured([instance])
+
+    with pytest.raises(AssertionError):
+        assert_only_unstructured({"key": instance})
+
+    with pytest.raises(AssertionError):
+        assert_only_unstructured((1, instance, 3))