Fix interpolate random (#4184)

* Fix interpolate random

* Make sure the test actually run

* remove unuse import

* fix float32 test

* formatting

* mark test xfailed on float32 as before

* add back import

Author: junpenglao

pymc3/distributions/continuous.py

@@ -4097,7 +4097,7 @@ def _argcdf(self, p):
     def _random(self, size=None):
         return self._argcdf(np.random.uniform(size=size))
 
-    def random(self, size=None):
+    def random(self, point=None, size=None):
         """
         Draw random values from Interpolated distribution.
 

pymc3/tests/test_distributions.py

@@ -174,7 +174,7 @@ def product(domains, n_samples=-1):
     try:
         names, domains = zip(*domains.items())
     except ValueError:  # domains.items() is empty
-        return []
+        return [{}]
     all_vals = [zip(names, val) for val in itertools.product(*[d.vals for d in domains])]
     if n_samples > 0 and len(all_vals) > n_samples:
         return (all_vals[j] for j in nr.choice(len(all_vals), n_samples, replace=False))