How to use the mdxpy.MdxHierarchySet.from_str function in mdxpy

def test_execute_mdx_without_columns(self):
        # write cube content
        self.tm1.cubes.cells.write_values(CUBE_NAME, self.cellset)

        # MDX Query that gets full cube content with zero suppression
        mdx = MdxBuilder.from_cube(CUBE_NAME) \
            .rows_non_empty().add_hierarchy_set_to_row_axis(
            MdxHierarchySet.all_members(DIMENSION_NAMES[0], DIMENSION_NAMES[0])) \
            .add_hierarchy_set_to_row_axis(MdxHierarchySet.all_members(DIMENSION_NAMES[1], DIMENSION_NAMES[1])) \
            .add_hierarchy_set_to_row_axis(MdxHierarchySet.all_members(DIMENSION_NAMES[2], DIMENSION_NAMES[2])) \
            .columns_non_empty().add_hierarchy_set_to_column_axis(MdxHierarchySet.from_str("", "", "{}")) \
            .to_mdx()

        data = self.tm1.cubes.cells.execute_mdx(mdx)
        # Check if total value is the same AND coordinates are the same. Handle None
        self.assertEqual(self.total_value, sum([v["Value"] for v in data.values() if v["Value"]]))
        for coordinates in data.keys():
            self.assertEqual(len(coordinates), 3)
            self.assertIn("[TM1py_Tests_Cell_Dimension1].", coordinates[0])
            self.assertIn("[TM1py_Tests_Cell_Dimension2].", coordinates[1])
            self.assertIn("[TM1py_Tests_Cell_Dimension3].", coordinates[2])

def test_execute_mdx_without_rows(self):
        # write cube content
        self.tm1.cubes.cells.write_values(CUBE_NAME, self.cellset)

        mdx = MdxBuilder.from_cube(CUBE_NAME) \
            .columns_non_empty() \
            .add_hierarchy_set_to_column_axis(MdxHierarchySet.all_members(DIMENSION_NAMES[0], DIMENSION_NAMES[0])) \
            .add_hierarchy_set_to_column_axis(MdxHierarchySet.all_members(DIMENSION_NAMES[1], DIMENSION_NAMES[1])) \
            .add_hierarchy_set_to_column_axis(MdxHierarchySet.all_members(DIMENSION_NAMES[2], DIMENSION_NAMES[2])) \
            .rows_non_empty() \
            .add_hierarchy_set_to_row_axis(MdxHierarchySet.from_str("", "", "{}")) \
            .to_mdx()

        data = self.tm1.cubes.cells.execute_mdx(mdx)
        # Check if total value is the same AND coordinates are the same. Handle None
        self.assertEqual(self.total_value, sum([v["Value"] for v in data.values() if v["Value"]]))
        for coordinates in data.keys():
            self.assertEqual(len(coordinates), 3)
            self.assertIn("[TM1py_Tests_Cell_Dimension1].", coordinates[0])
            self.assertIn("[TM1py_Tests_Cell_Dimension2].", coordinates[1])
            self.assertIn("[TM1py_Tests_Cell_Dimension3].", coordinates[2])