Fix flaky test poisson generator & test_negative_binomial_generator (a…

…pache#14571)

* set success_rate to 0.2

* fix the flaky test

* reenable the test

python/mxnet/test_utils.py

@@ -1926,7 +1926,7 @@ def chi_square_check(generator, buckets, probs, nsamples=1000000):
     _, p = ss.chisquare(f_obs=obs_freq, f_exp=expected_freq)
     return p, obs_freq, expected_freq
 
-def verify_generator(generator, buckets, probs, nsamples=1000000, nrepeat=5, success_rate=0.25, alpha=0.05):
+def verify_generator(generator, buckets, probs, nsamples=1000000, nrepeat=5, success_rate=0.2, alpha=0.05):
     """Verify whether the generator is correct using chi-square testing.
 
     The test is repeated for "nrepeat" times and we check if the success rate is

tests/python/unittest/test_random.py

@@ -568,7 +568,6 @@ def test_exponential_generator():
                      for _ in range(10)])
             verify_generator(generator=generator_mx_same_seed, buckets=buckets, probs=probs, success_rate=0.20)
 
-@unittest.skip("Flaky test. Tracked in https://github.com/apache/incubator-mxnet/issues/13584")
 @with_seed()
 def test_poisson_generator():
     ctx = mx.context.current_context()
@@ -584,7 +583,6 @@ def test_poisson_generator():
                      for _ in range(10)])
             verify_generator(generator=generator_mx_same_seed, buckets=buckets, probs=probs)
 
-@unittest.skip("Flaky test. Tracked in https://github.com/apache/incubator-mxnet/issues/13506")
 @with_seed()
 def test_negative_binomial_generator():
     ctx = mx.context.current_context()