code: def test_get_common_suffix():
      df = pd.DataFrame(
          {
              "prompt": [f"prompt{i} answer:" for i in range(100)],
              "completion": [f"completion{i}" for i in range(100)],
              "empty_completion": [""] * 100,
              "some_empty_completion": ["", "completion"] * 50,
          }
      )
      assert get_common_suffix(df.prompt) == " answer:"
      assert get_common_suffix(df.completion) == ""
      assert get_common_suffix(df.empty_completion) == ""
      assert get_common_suffix(df.some_empty_completion) == ""
  
imports: import pandas
  import pytest
  from ..customization_dataset_preparation import convert_into_prompt_completion_only, convert_into_template, drop_duplicated_rows, drop_unrequired_fields, get_common_suffix, get_prepared_filename, parse_template, recommend_hyperparameters, show_first_example_in_df, split_into_train_validation, template_mapper, validate_template, warn_and_drop_long_samples, warn_completion_is_not_empty, warn_duplicated_rows, warn_imbalanced_completion, warn_low_n_samples, warn_missing_suffix
label_desc: Use image node_id 4 for calling a global function with example usage: test_get_common_suffix() without return types