code: def test_flat_values(self):
      dtype = np.float64
      interval_times = np.array(
          [0.3, 1.0, 1.43, 3.7, 9.2, 12.48], dtype=dtype
      )
      interval_values = np.array([8.0] * 6, dtype=dtype)
      test_times = tf.constant(
          [0.1, 1.1, 1.22, 0.45, 1.8, 3.8, 7.45, 7.73, 9.6, 11.7, 12.0],
          dtype=dtype,
      )
      actual, _ = self.evaluate(
          monotone_convex.interpolate(
              test_times, interval_values, interval_times
          )
      )
      expected = np.zeros([11], dtype=dtype) + 8.0
      np.testing.assert_allclose(actual, expected)
  
imports: from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v2
  from tensorflow.python.framework import test_util
  from tf_quant_finance.rates.hagan_west import monotone_convex
label_desc: Use image node_id 6 for calling the MonotoneConvexTest obj's underlying member method code with example usage: obj.test_flat_values() without return types