Merge pull request #396 from sylvesterkaczmarek:fix/validate-sanctioner-alternating-steps

PiperOrigin-RevId: 969328287
Change-Id: Id4c48c5847bfdb4966a620d8e0a0b2fa6c28ad10

Author: copybara-github

meltingpot/utils/puppeteers/clean_up.py

@@ -304,7 +304,10 @@ def __init__(
     self._threshold = threshold
     self._recency_window = recency_window
 
-    self._alternating_steps = alternating_steps
+    if alternating_steps > 0:
+      self._alternating_steps = alternating_steps
+    else:
+      raise ValueError('alternating_steps must be positive')
     self._nice = nice
 
     self._steps_to_sanction_when_motivated = steps_to_sanction_when_motivated

meltingpot/utils/puppeteers/sanctioner_alternator_validation_test.py

@@ -0,0 +1,39 @@
+# Copyright 2026 DeepMind Technologies Limited.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Validation tests for SanctionerAlternator."""
+
+from unittest import mock
+
+from absl.testing import absltest
+from absl.testing import parameterized
+from meltingpot.utils.puppeteers import clean_up
+
+
+class SanctionerAlternatorValidationTest(parameterized.TestCase):
+
+  @parameterized.parameters(0, -1)
+  def test_rejects_nonpositive_alternating_steps(self, alternating_steps):
+    with self.assertRaisesRegex(ValueError, 'alternating_steps must be positive'):
+      clean_up.SanctionerAlternator(
+          cooperate_goal=mock.sentinel.cooperate,
+          defect_goal=mock.sentinel.defect,
+          sanction_goal=mock.sentinel.sanction,
+          num_others_cooperating_cumulant='NUM_OTHERS_COOPERATING',
+          threshold=1,
+          alternating_steps=alternating_steps,
+      )
+
+
+if __name__ == '__main__':
+  absltest.main()