Add test for serializing extension attrs (see #1085)

spacy/tests/serialize/test_serialize_extension_attrs.py

@@ -0,0 +1,27 @@
+# coding: utf-8
+from __future__ import unicode_literals
+
+import pytest
+
+from ...tokens.doc import Doc
+from ...vocab import Vocab
+
+
+@pytest.fixture
+def doc_w_attrs(en_tokenizer):
+    Doc.set_extension('_test_attr', default=False)
+    Doc.set_extension('_test_prop', getter=lambda doc: len(doc.text))
+    Doc.set_extension('_test_method', method=lambda doc, arg: "{}{}".format(len(doc.text), arg))
+    doc = en_tokenizer("This is a test.")
+    doc._._test_attr = 'test'
+    return doc
+
+
+
+def test_serialize_ext_attrs_from_bytes(doc_w_attrs):
+    doc_b = doc_w_attrs.to_bytes()
+    doc = Doc(Vocab()).from_bytes(doc_b)
+    assert doc._.has('_test_attr')
+    assert doc._._test_attr == 'test'
+    assert doc._._test_prop == len(doc.text)
+    assert doc._._test_method('test') == '{}{}'.format(len(doc.text), 'test')