diff --git a/spacy/tests/test_underscore.py b/spacy/tests/test_underscore.py
new file mode 100644
index 000000000..262098515
--- /dev/null
+++ b/spacy/tests/test_underscore.py
@@ -0,0 +1,50 @@
+from mock import Mock
+from ..tokens.underscore import Underscore
+
+
+def test_create_doc_underscore():
+    doc = Mock()
+    doc.doc = doc
+    uscore = Underscore(Underscore.doc_extensions, doc)
+    assert uscore._doc is doc
+    assert uscore._start is None
+    assert uscore._end is None
+
+def test_doc_underscore_getattr_setattr():
+    doc = Mock()
+    doc.doc = doc
+    doc.user_data = {}
+    Underscore.doc_extensions['hello'] = (False, None, None, None)
+    doc._ = Underscore(Underscore.doc_extensions, doc)
+    assert doc._.hello == False
+    doc._.hello = True
+    assert doc._.hello == True
+
+def test_create_span_underscore():
+    span = Mock(doc=Mock(), start=0, end=2)
+    uscore = Underscore(Underscore.span_extensions, span,
+                        start=span.start, end=span.end)
+    assert uscore._doc is span.doc
+    assert uscore._start is span.start
+    assert uscore._end is span.end
+
+def test_span_underscore_getter_setter():
+    span = Mock(doc=Mock(), start=0, end=2)
+    Underscore.span_extensions['hello'] = (None, None,
+                                           lambda s: (s.start, 'hi'),
+                                           lambda s, value: setattr(s, 'start',
+                                                                    value))
+    span._ = Underscore(Underscore.span_extensions, span,
+                        start=span.start, end=span.end)
+ 
+    assert span._.hello == (0, 'hi')
+    span._.hello = 1
+    assert span._.hello == (1, 'hi')
+
+
+def test_token_underscore_method():
+    token = Mock(doc=Mock(), idx=7, say_cheese=lambda: 'cheese')
+    Underscore.token_extensions['hello'] = (None, token.say_cheese,
+                                            None, None)
+    token._ = Underscore(Underscore.token_extensions, token, start=token.idx)
+    assert token._.hello() == 'cheese'