code: def testZeroRate(self):
      lam = self.dtype(0.0)
      dist = skellam.Skellam(rate1=lam, rate2=lam, validate_args=True)
      self.assertAllClose(lam, self.evaluate(dist.rate1))
      self.assertAllClose(lam, self.evaluate(dist.rate2))
      self.assertAllClose(0.0, dist.prob(3.0))
      self.assertAllClose(1.0, dist.prob(0.0))
      self.assertAllClose(0.0, dist.log_prob(0.0))
  
imports: import numpy
  from scipy import stats
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import skellam
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import gradient
label_desc: Use image node_id 4 for calling the _SkellamTest obj's underlying member method code with example usage: obj.testZeroRate() without return types