copy random states when combining random variables (#207)

src/probnum/utils/randomutils.py

@@ -1,14 +1,17 @@
 from typing import Union
+import copy
 
 import numpy as np
 
 
 def derive_random_seed(*args: Union[np.random.RandomState, np.random.Generator]) -> int:
     def _sample(rng: Union[np.random.RandomState, np.random.Generator]) -> int:
         if isinstance(rng, np.random.RandomState):
-            return rng.randint(0, 2 ** 32, size=None, dtype=int)
+            return copy.copy(rng).randint(0, 2 ** 32, size=None, dtype=int)
         elif isinstance(rng, np.random.Generator):
-            return rng.integers(0, 2 ** 32, size=None, dtype=int, endpoint=False)
+            return copy.copy(rng).integers(
+                0, 2 ** 32, size=None, dtype=int, endpoint=False
+            )
         else:
             raise ValueError("Unsupported type of random number generator")
 

tests/test_utils/test_fctutils.py

@@ -6,6 +6,8 @@
 
 
 class TestAssertsEvaluatesToScalar(unittest.TestCase):
+    """Test case for utility functions dealing with functions."""
+
     def test_assert_evaluates_to_scalar_pass(self):
         def fct(x):
             return np.linalg.norm(x)

tests/test_utils/test_randomutils.py

@@ -0,0 +1,46 @@
+import unittest
+
+import numpy as np
+
+from tests.testing import NumpyAssertions
+from probnum.utils import randomutils
+
+
+class RandomUtilsTestCase(unittest.TestCase, NumpyAssertions):
+    """Test case for utility functions handling objects dealing with randomness."""
+
+    def setUp(self) -> None:
+        self.seed = 42
+        self.random_state = np.random.RandomState(seed=self.seed)
+        self.random_generator = np.random.default_rng(seed=self.seed)
+        self.random_generator_list = [np.random.default_rng(seed=s) for s in range(5)]
+
+    def test_derive_random_seed_invariant_random_state(self):
+        """
+        Test whether deriving a random seed leaves the original random states
+        untouched.
+        """
+        # Original random states
+        rs_state = self.random_state.get_state()[1]
+        rng_state = self.random_generator.bit_generator.state["state"]["state"]
+        rng_list_states = [
+            rng.bit_generator.state["state"]["state"]
+            for rng in self.random_generator_list
+        ]
+
+        # Combine RandomState and Generator object
+        _ = randomutils.derive_random_seed(self.random_state, self.random_generator)
+        self.assertArrayEqual(rs_state, self.random_state.get_state()[1])
+        self.assertEqual(
+            rng_state, self.random_generator.bit_generator.state["state"]["state"]
+        )
+
+        # Combine list of generators
+        _ = randomutils.derive_random_seed(*self.random_generator_list)
+        self.assertArrayEqual(
+            rng_list_states,
+            [
+                rng.bit_generator.state["state"]["state"]
+                for rng in self.random_generator_list
+            ],
+        )