Add a model based using 'attrs' and Hypothesis strategies to generate it.

---

Migrated from D1360 (view on Phabricator)

swh/model/tests/test_hypothesis_strategies.py

+# Copyright (C) 2019 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import attr
+from hypothesis import given
+
+from swh.model.hashutil import DEFAULT_ALGORITHMS
+from swh.model.hypothesis_strategies import objects, object_dicts
+
+
+target_types = (
+    'content', 'directory', 'revision', 'release', 'snapshot', 'alias')
+
+
+@given(objects())
+def test_generation(obj_type_and_obj):
+    (obj_type, object_) = obj_type_and_obj
+    attr.validate(object_)
+
+
+@given(object_dicts())
+def test_dicts_generation(obj_type_and_obj):
+    (obj_type, object_) = obj_type_and_obj
+    assert isinstance(object_, dict)
+    if obj_type == 'content':
+        if object_['status'] == 'visible':
+            assert set(object_) == \
+                set(DEFAULT_ALGORITHMS) | {'length', 'status', 'data'}
+        else:
+            assert set(object_) == \
+                set(DEFAULT_ALGORITHMS) | {'length', 'status'}
+    elif obj_type == 'release':
+        assert object_['target_type'] in target_types
+    elif obj_type == 'snapshot':
+        for branch in object_['branches'].values():
+            assert branch['target_type'] in target_types