code: def test_all_strings(self):
      features = ["a", "b", "c"]
      processed_features = [
          ("a", dt.Double()),
          ("b", dt.Double()),
          ("c", dt.Double()),
      ]
      out = fm.process_or_validate_features(features)
      self.assertEqual(out, processed_features)
      self.assertTrue(fm.is_valid_feature_list(out))
  
file_path: coremltools/coremltools/test/sklearn_tests/test_feature_names.py
imports: import unittest
  import coremltools.models._feature_management
  import coremltools.models.datatypes
  from coremltools._deps import _HAS_SKLEARN
label_desc: Use image node_id 1 for calling the FeatureManagementTests obj's underlying member method code with example usage: obj.test_all_strings() without return types