Add tests for pickling doc

spacy/tests/doc/test_pickle_doc.py

@@ -0,0 +1,25 @@
+from __future__ import unicode_literals
+
+import pickle
+
+from ...language import Language
+
+
+def test_pickle_single_doc():
+    nlp = Language()
+    doc = nlp(u'pickle roundtrip')
+    data = pickle.dumps(doc, 1)
+    doc2 = pickle.loads(data)
+    assert doc2.text == 'pickle roundtrip'
+
+
+def test_list_of_docs_pickles_efficiently():
+    nlp = Language()
+    one_pickled = pickle.dumps(nlp(u'0'), -1)
+    docs = list(nlp.pipe(str(i) for i in range(100)))
+    many_pickled = pickle.dumps(docs, -1)
+    assert len(many_pickled) < (len(one_pickled) * 2)
+    many_unpickled = pickle.loads(many_pickled)
+    assert many_unpickled[0].text == '0'
+    assert many_unpickled[-1].text == '99'
+    assert len(many_unpickled) == 99