add regression test for issue 3965 (#3979)

* add regression test for issue 3965
* pass on the tune argument to fix #3965

closes #3965

Author: michaelosthege

pymc3/step_methods/hmc/quadpotential.py

@@ -307,7 +307,7 @@ def update(self, sample, grad, tune):
         self._ngrads2 += 1
 
         if self._n_samples <= 150:
-            super().update(sample, grad)
+            super().update(sample, grad, tune)
         else:
             self._update((self._ngrads1 / self._grads1) ** 2)
 

pymc3/tests/test_quadpotential.py

@@ -283,3 +283,9 @@ def test_full_adapt_sampling(seed=289586):
         pymc3.sample(
             draws=10, tune=1000, random_seed=seed, step=step, cores=1, chains=1
         )
+
+        
+def test_issue_3965():
+    with pymc3.Model():
+        pymc3.Normal('n')
+        pymc3.sample(100, tune=300, chains=1, init='advi+adapt_diag_grad')