code: def test_constant(self):
      lr_fn = lr_schedules.constant(0.02)
      self.assertEqual(0.02, lr_fn(1))
      self.assertEqual(0.02, lr_fn(20))
      self.assertEqual(0.02, lr_fn(300))
      self.assertEqual(0.02, lr_fn(4000))
      self.assertEqual(0.02, lr_fn(50000))
      self.assertEqual(0.02, lr_fn(600000))
      self.assertEqual(0.02, lr_fn(7000000))
      self.assertEqual(0.02, lr_fn(80000000))
      self.assertEqual(0.02, lr_fn(900000000))
  
file_path: trax/trax/supervised/lr_schedules_test.py
imports: import math
  from absl.testing import absltest
  from trax.supervised import lr_schedules
label_desc: Use image node_id 2 for calling the LRFunctionsTest obj's underlying member method code with example usage: obj.test_constant() without return types