[hidden trouble] Update test_sparse_transpose_op.py to get rid of a h…

…idden trouble. (PaddlePaddle#47017)

* Update test_sparse_transpose_op.py

* Update test_sparse_transpose_op.py

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

@@ -23,7 +23,9 @@ class TestTranspose(unittest.TestCase):
     def check_result(self, x_shape, dims, format):
         with _test_eager_guard():
             mask = paddle.randint(0, 2, x_shape).astype("float32")
-            origin_x = paddle.rand(x_shape, dtype='float32') * mask
+            # "+ 1" to make sure that all zero elements in "origin_x" is caused by multiplying by "mask",
+            # or the backward checks may fail.
+            origin_x = (paddle.rand(x_shape, dtype='float32') + 1) * mask
             dense_x = origin_x.detach()
             dense_x.stop_gradient = False
             dense_out = paddle.transpose(dense_x, dims)