class_docstr: string utils test
docstr: test lower string
docstr_tok: ["test","lower","string"]
code: def test_lower(self):
      """test lower string"""
      with self.cached_session(use_gpu=False, force_gpu=False):
          output = py_x_ops.str_lower("Hello WORLD").eval()
          self.assertEqual(b"hello world", output)
          output = py_x_ops.str_lower(["Hello WORLD", "ABC XYZ"]).eval()
          self.assertAllEqual([b"hello world", b"abc xyz"], output)
  
imports: import delta.compat
  from delta.layers.ops import py_x_ops
label_desc: Use image node_id 3 for calling the StringUtilsOpTest obj's underlying member method code with example usage: obj.test_lower() without return types