Add check of input in sequence_expand op. (#15466)

* Add check of input in sequence_expand op.
test=develop

* Correct the unittest of sequence_expand op.
test=develop

paddle/fluid/operators/sequence_ops/sequence_expand_op.cc

@@ -68,6 +68,11 @@ class SequenceExpandOp : public framework::OperatorWithKernel {
                        "Level number of Input(X)'s lod could be 0. Otherwise "
                        "size of Input(X)'s first level lod should be equal to "
                        "size of Input(Y)'s referred level lod.");
+      } else {
+        PADDLE_ENFORCE_EQ(x_dims[0], y_lod[ref_level].size() - 1,
+                          "When Input(X)'s lod is null, the dims[0] of "
+                          "Input(X) should match the "
+                          "size of Input(Y)'s referred level lod.");
       }
 
       int64_t out_first_dim = 0;

python/paddle/fluid/tests/unittests/test_sequence_expand.py

@@ -81,11 +81,10 @@ class TestSequenceExpand(OpTest):
 class TestSequenceExpandCase1(TestSequenceExpand):
     def set_data(self):
         x_data = np.random.uniform(0.1, 1, [5, 1]).astype('float32')
-        x_lod = [[2, 3]]
         y_data = np.random.uniform(0.1, 1, [13, 1]).astype('float32')
         y_lod = [[2, 3], [2, 2, 3, 3, 3]]
         self.inputs = {'X': x_data, 'Y': (y_data, y_lod)}
-        self.attrs = {'ref_level': 0}
+        self.attrs = {'ref_level': 1}
 
 
 class TestSequenceExpandCase2(TestSequenceExpand):