Add unit test case for no tokens to be erased

python/paddle/v2/fluid/tests/test_sequence_erase_op.py

@@ -44,5 +44,20 @@ class TestSequenceEraseOp(OpTest):
         self.check_output()
 
 
+class TestSequenceEraseOpEmpty(OpTest):
+    def setUp(self):
+        self.op_type = "sequence_erase"
+        in_seq = np.random.randint(0, 10, (30, 1)).astype("int32")
+        lod = [[0, 9, 13, 24, 30]]
+        tokens = []
+        out_seq, new_lod0 = sequence_erase(in_seq, lod[0], tokens)
+        self.attrs = {'tokens': tokens}
+        self.inputs = {'X': (in_seq, lod)}
+        self.outputs = {'Out': (out_seq, [new_lod0])}
+
+    def test_check_output(self):
+        self.check_output()
+
+
 if __name__ == '__main__':
     unittest.main()