Unit test for Issue 3879 (#4153)

* failing unit test for Issue #3879

* mark test as failing

spacy/tests/regression/test_issue3879.py

@@ -0,0 +1,21 @@
+# coding: utf8
+from __future__ import unicode_literals
+
+import pytest
+from spacy.lang.en import English
+from spacy.matcher import Matcher
+
+
+@pytest.mark.xfail
+def test_issue3879(en_vocab):
+    nlp = English()
+    text = "This is a test."
+    doc = nlp(text)
+    assert len(doc) == 5
+
+    pattern = [{"ORTH": "This", "OP": "?"}, {"OP": "?"}, {"ORTH": "test"}]
+    matcher = Matcher(nlp.vocab)
+    matcher.add("rule", None, pattern)
+    matches = matcher(doc)
+
+    assert len(matches) == 2  # fails because of a FP match 'is a test'