code: def test_from_nested_to_long(n_instances, n_columns, n_timepoints):
      """Test from_nested_to_long for correctness."""
      nested, _ = make_classification_problem(
          n_instances, n_columns, n_timepoints
      )
      X_long = from_nested_to_long(
          nested,
          instance_column_name="case_id",
          time_column_name="reading_id",
          dimension_column_name="dim_id",
      )
  
      assert isinstance(X_long, pd.DataFrame)
      assert X_long.shape == (n_instances * n_timepoints * n_columns, 4)
      assert (
          X_long.columns == ["case_id", "reading_id", "dim_id", "value"]
      ).all()
  
imports: import numpy
  import pandas
  import pytest
  from sktime.datasets import generate_example_long_table, make_multi_index_dataframe
  from sktime.datatypes._adapter import convert_from_multiindex_to_listdataset
  from sktime.datatypes._panel._check import are_columns_nested, is_nested_dataframe
  from sktime.datatypes._panel._convert import from_2d_array_to_nested, from_3d_numpy_to_2d_array, from_3d_numpy_to_multi_index, from_3d_numpy_to_nested, from_long_to_nested, from_multi_index_to_3d_numpy, from_multi_index_to_nested, from_nested_to_2d_array, from_nested_to_3d_numpy, from_nested_to_long, from_nested_to_multi_index
  from sktime.utils._testing.panel import make_classification_problem
  from sktime.utils.validation._dependencies import _check_soft_dependencies
label_desc: Use image node_id 13 for calling a global function with example usage: test_from_nested_to_long(n_instances, n_columns, n_timepoints) without return types