Test Issue #588: Matcher accepts invalid, empty patterns.

spacy/tests/regression/test_issue588.py

@@ -0,0 +1,10 @@
+import pytest
+from ...vocab import Vocab
+from ...tokens import Doc
+from ...matcher import Matcher
+
+
+def test_issue588():
+    matcher = Matcher(Vocab())
+    with pytest.raises(ValueError):
+        matcher.add(entity_key='1', label='TEST', attrs={}, specs=[[]])