code: def test_seed_per_observation_with_only_1_variable_as_seed(df_na):
      # test case 4: observation seed, only variable indicated as seed, method: addition
      # Note the variable used as seed should not have missing data
      df_na = df_na.copy()
      df_na["Age"] = df_na["Age"].fillna(1)
  
      imputer = RandomSampleImputer(
          variables=["City", "Studies"],
          random_state="Age",
          seed="observation",
      )
  
      X_transformed = imputer.fit_transform(df_na)
  
      # expected output
      ref = {
          "Name": [
              "tom",
              "nick",
              "krish",
              np.nan,
              "peter",
              np.nan,
              "fred",
              "sam",
          ],
          "City": [
              "London",
              "Manchester",
              "Manchester",
              "Manchester",
              "London",
              "London",
              "Bristol",
              "Manchester",
          ],
          "Studies": [
              "Bachelor",
              "Bachelor",
              "Masters",
              "Masters",
              "Bachelor",
              "PhD",
              "None",
              "Masters",
          ],
          "Age": [20, 21, 19, np.nan, 23, 40, 41, 37],
          "Marks": [0.9, 0.8, 0.7, np.nan, 0.3, np.nan, 0.8, 0.6],
          "dob": pd.date_range("2020-02-24", periods=8, freq="T"),
      }
      ref = pd.DataFrame(ref)
  
      assert imputer.random_state == ["Age"]
  
      pd.testing.assert_frame_equal(
          imputer.X_[["City", "Studies"]], df_na[["City", "Studies"]]
      )
  
      pd.testing.assert_frame_equal(
          X_transformed[["City", "Studies"]],
          ref[["City", "Studies"]],
          check_dtype=False,
      )
  
file_path: feature_engine/tests/test_imputation/test_random_sample_imputer.py
imports: import numpy
  import pandas
  import pytest
  from feature_engine.imputation import RandomSampleImputer
  from feature_engine.imputation.random_sample import _define_seed
label_desc: Use image node_id 5 for calling a global function with example usage: test_seed_per_observation_with_only_1_variable_as_seed(df_na) without return types