* Add tests for string intern

tests/test_intern.py

@@ -0,0 +1,35 @@
+# -*- coding: utf8 -*-
+from __future__ import unicode_literals
+
+from spacy.utf8string import StringStore
+
+import pytest
+
+@pytest.fixture
+def sstore():
+    return StringStore()
+
+def test_save_bytes(sstore):
+    Hello_i = sstore[b'Hello']
+    assert Hello_i == 1
+    assert sstore[b'Hello'] == 1
+    assert sstore[b'goodbye'] != Hello_i
+    assert sstore[b'hello'] != Hello_i
+    assert Hello_i == 1
+
+
+def test_save_unicode(sstore):
+    with pytest.raises(TypeError):
+        A_i = sstore['A']
+
+
+def test_zero_id(sstore):
+    with pytest.raises(IndexError):
+        sstore[0]
+
+def test_retrieve_id(sstore):
+    A_i = sstore[b'A']
+    assert sstore.size == 1
+    assert sstore[1] == b'A'
+    with pytest.raises(IndexError):
+        sstore[2]