fix a bug in test_batch_norm_op.py (#10094)

Author: luotao1

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

@@ -100,6 +100,9 @@ def _reference_grad(x, y_grad, scale, mean, var, epsilon, data_format):
     #   (x - mean) * sum(grad_y * (x - mean)) / (var + epsilon))
 
     # transfer from (N, C, H, W) to (N, H, W, C) to simplify computation
+    if data_format != "NCHW" and data_format != "NHWC":
+        raise ValueError("Unknown data order.")
+
     if data_format == "NCHW":
         x = np.transpose(x, (0, 2, 3, 1))
         y_grad = np.transpose(y_grad, (0, 2, 3, 1))
@@ -304,7 +307,7 @@ def test_with_place(place, data_layout, shape):
             # run backward
             y_grad = np.random.random_sample(shape).astype(np.float32)
             x_grad, scale_grad, bias_grad = _reference_grad(
-                x, y_grad, scale, saved_mean, var_ref, epsilon, data_format)
+                x, y_grad, scale, saved_mean, var_ref, epsilon, data_layout)
 
             var_dict = locals()
             var_dict['y@GRAD'] = y_grad