Added random_seed argument to the sampler in some MLDA tests (#4313)

Author: mikkelbue

pymc3/tests/test_step.py

@@ -1133,7 +1133,7 @@ def test_nonparallelized_chains_are_random(self):
             Normal("x", 0, 1)
             for stepper in TestMLDA.steppers:
                 step = stepper(coarse_models=[coarse_model])
-                trace = sample(chains=2, cores=1, draws=20, tune=0, step=step)
+                trace = sample(chains=2, cores=1, draws=20, tune=0, step=step, random_seed=1)
                 samples = np.array(trace.get_values("x", combine=False))[:, 5]
                 assert (
                     len(set(samples)) == 2
@@ -1150,7 +1150,7 @@ def test_parallelized_chains_are_random(self):
             Normal("x", 0, 1)
             for stepper in TestMLDA.steppers:
                 step = stepper(coarse_models=[coarse_model])
-                trace = sample(chains=2, cores=2, draws=20, tune=0, step=step)
+                trace = sample(chains=2, cores=2, draws=20, tune=0, step=step, random_seed=1)
                 samples = np.array(trace.get_values("x", combine=False))[:, 5]
                 assert len(set(samples)) == 2, "Parallelized {} " "chains are identical.".format(
                     stepper
@@ -1176,7 +1176,7 @@ def test_acceptance_rate_against_coarseness(self):
             Normal("x", 5.0, 1.0)
             for coarse_model in possible_coarse_models:
                 step = MLDA(coarse_models=[coarse_model], subsampling_rates=3)
-                trace = sample(chains=1, draws=500, tune=100, step=step)
+                trace = sample(chains=1, draws=500, tune=100, step=step, random_seed=1)
                 acc.append(trace.get_sampler_stats("accepted").mean())
             assert acc[0] > acc[1] > acc[2], (
                 "Acceptance rate is not "