code: def test_preserves_types(self):
      self.pipeline = tests.mocks.pipelines.Users()
      training_data = pandas.concat(
          [chunk for chunk in self.pipeline.training_data]
      )
      self.assertTrue(training_data["id"].dtype, "integer")
      self.assertTrue(training_data["first_name"].dtype, "object")
      self.assertTrue(training_data["last_name"].dtype, "object")
      self.assertTrue(training_data["subscriber"].dtype, "bool")
      self.assertTrue(
          training_data["signup_at"].dtype, "datetime64[ns]"
      )
  
file_path: lore/tests/unit/test_pipelines.py
imports: from __future__ import generators
  import unittest
  import pandas
  import tests.mocks.pipelines
label_desc: Use image node_id 9 for calling the TestLowMemory obj's underlying member method code with example usage: obj.test_preserves_types() without return types