Add test

tests/test_mecab.py

@@ -320,6 +320,18 @@ def test_parse_tonodes_boundary(self):
                 if not node.is_eos():
                     self.assertEqual(node.feature, expected[i])
 
+        with mecab.MeCab(r'-O "" -F%m\s%s') as nm:
+            # with empty string option
+            yml1 = self.yaml.get('text5')
+            txt1 = self._u2str(yml1.get('text'))
+            pat1 = self._u2str(yml1.get('pattern'))
+            expected = [self._u2str(e) for e in yml1.get('expected')]
+
+            gen = nm.parse(txt1, boundary_constraints=pat1, as_nodes=True)
+            for i, node in enumerate(gen):
+                if not node.is_eos():
+                    self.assertEqual(node.feature, expected[i])
+
         with mecab.MeCab(r'-F%m\s%F\s[0,1]\s%s -N2') as nm:
             # with N-best and output formatting
             yml1 = self.yaml.get('text6')