Feature/better simple classes (#119)

tests/test_funcs.py

@@ -132,10 +132,13 @@ class TestAsDict(object):
         } == res
         assert isinstance(res, dict_factory)
 
-    @given(simple_classes(), st.sampled_from(MAPPING_TYPES))
+    @given(simple_classes(private_attrs=False), st.sampled_from(MAPPING_TYPES))
     def test_roundtrip(self, cls, dict_class):
         """
         Test dumping to dicts and back for Hypothesis-generated classes.
+
+        Private attributes don't round-trip (the attribute name is different
+        than the initializer argument).
         """
         instance = cls()
         dict_instance = asdict(instance, dict_factory=dict_class)
@@ -359,22 +362,27 @@ class TestAssoc(object):
         assert i1 is not i2
         assert i1 == i2
 
-    @given(simple_classes(), st.integers())
-    def test_change(self, C, val):
+    @given(simple_classes(), st.data())
+    def test_change(self, C, data):
         """
         Changes work.
         """
         # Take the first attribute, and change it.
         assume(fields(C))  # Skip classes with no attributes.
+        field_names = [a.name for a in fields(C)]
         original = C()
-        attribute = fields(C)[0]
-        changed = assoc(original, **{attribute.name: val})
-        assert getattr(changed, attribute.name) == val
+        chosen_names = data.draw(st.sets(st.sampled_from(field_names)))
+        change_dict = {name: data.draw(st.integers())
+                       for name in chosen_names}
+        changed = assoc(original, **change_dict)
+        for k, v in change_dict.items():
+            assert getattr(changed, k) == v
 
     @given(simple_classes())
     def test_unknown(self, C):
         """
-        Wanting to change an unknown attribute raises a ValueError.
+        Wanting to change an unknown attribute raises an
+        AttrsAttributeNotFoundError.
         """
         # No generated class will have a four letter attribute.
         with pytest.raises(AttrsAttributeNotFoundError) as e:

tests/utils.py

@@ -74,6 +74,16 @@ def gen_attr_names():
             yield outer + inner
 
 
+def maybe_underscore_prefix(source):
+    """
+    A generator to sometimes prepend an underscore.
+    """
+    to_underscore = False
+    for val in source:
+        yield val if not to_underscore else '_' + val
+        to_underscore = not to_underscore
+
+
 def _create_hyp_class(attrs):
     """
     A helper function for Hypothesis to generate attrs classes.
@@ -164,7 +174,7 @@ list_of_attrs = st.lists(simple_attrs, average_size=3, max_size=9)
 
 
 @st.composite
-def simple_classes(draw, slots=None, frozen=None):
+def simple_classes(draw, slots=None, frozen=None, private_attrs=None):
     """
     A strategy that generates classes with default non-attr attributes.
 
@@ -173,21 +183,32 @@ def simple_classes(draw, slots=None, frozen=None):
     @attr.s(slots=True, frozen=True)
     class HypClass:
         a = attr.ib(default=1)
-        b = attr.ib(default=None)
+        _b = attr.ib(default=None)
         c = attr.ib(default='text')
-        d = attr.ib(default=1.0)
+        _d = attr.ib(default=1.0)
         c = attr.ib(default={'t': 1})
 
     By default, all combinations of slots and frozen classes will be generated.
     If `slots=True` is passed in, only slots classes will be generated, and
     if `slots=False` is passed in, no slot classes will be generated. The same
     applies to `frozen`.
+
+    By default, some attributes will be private (i.e. prefixed with an
+    underscore). If `private_attrs=True` is passed in, all attributes will be
+    private, and if `private_attrs=False`, no attributes will be private.
     """
     attrs = draw(list_of_attrs)
     frozen_flag = draw(st.booleans()) if frozen is None else frozen
     slots_flag = draw(st.booleans()) if slots is None else slots
 
-    cls_dict = dict(zip(gen_attr_names(), attrs))
+    if private_attrs is None:
+        attr_names = maybe_underscore_prefix(gen_attr_names())
+    elif private_attrs is True:
+        attr_names = ('_' + n for n in gen_attr_names())
+    elif private_attrs is False:
+        attr_names = gen_attr_names()
+
+    cls_dict = dict(zip(attr_names, attrs))
     post_init_flag = draw(st.booleans())
     if post_init_flag:
         def post_init(self):