chore: import upstream snapshot with attribution

tests/unittests/evaluation/simulation/test_user_simulator.py

@@ -0,0 +1,106 @@
+# Copyright 2026 Google LLC
+#
+# 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
+#
+#     http://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.
+
+from __future__ import annotations
+
+from google.adk.evaluation.simulation import user_simulator as user_simulator_module
+from google.adk.evaluation.simulation.user_simulator import BaseUserSimulatorConfig
+from google.adk.evaluation.simulation.user_simulator import NextUserMessage
+from google.adk.evaluation.simulation.user_simulator import register_user_simulator
+from google.adk.evaluation.simulation.user_simulator import Status
+from google.adk.evaluation.simulation.user_simulator import UserSimulator
+from google.genai.types import Content
+from pydantic import Field
+import pytest
+from typing_extensions import Literal
+
+
+def test_next_user_message_validation():
+  """Tests post-init validation of NextUserMessage."""
+  with pytest.raises(
+      ValueError,
+      match=(
+          "A user_message should be provided if and only if the status is"
+          " SUCCESS"
+      ),
+  ):
+    NextUserMessage(status=Status.SUCCESS)
+
+  with pytest.raises(
+      ValueError,
+      match=(
+          "A user_message should be provided if and only if the status is"
+          " SUCCESS"
+      ),
+  ):
+    NextUserMessage(status=Status.TURN_LIMIT_REACHED, user_message=Content())
+
+  # these two should not cause exceptions
+  NextUserMessage(status=Status.SUCCESS, user_message=Content())
+  NextUserMessage(status=Status.TURN_LIMIT_REACHED)
+
+
+# -----------------------------------------------------------------------------
+# `register_user_simulator` -- the extension-point API in `user_simulator.py`.
+# End-to-end dispatch through `UserSimulatorProvider` is covered separately in
+# `test_user_simulator_provider.py`.
+# -----------------------------------------------------------------------------
+
+
+class _FakeConfig(BaseUserSimulatorConfig):
+  """Test-only config subclass with a unique Literal discriminator."""
+
+  type: Literal["fake_sim"] = Field(default="fake_sim")
+
+
+class _FakeSimulator(UserSimulator):
+  """Test-only simulator; internals do not matter, only its type identity."""
+
+
+def test_register_user_simulator_writes_to_shared_registry():
+  """`register_user_simulator(config_type, simulator_type)` must write the
+
+  mapping into `_SIMULATOR_BY_CONFIG_TYPE` so that any consumer -- including
+  `UserSimulatorProvider` in another module -- can look it up.
+  """
+  try:
+    register_user_simulator(_FakeConfig, _FakeSimulator)
+    assert (
+        user_simulator_module._SIMULATOR_BY_CONFIG_TYPE.get(_FakeConfig)
+        is _FakeSimulator
+    )
+  finally:
+    # Clean up so we don't leak state into other tests.
+    user_simulator_module._SIMULATOR_BY_CONFIG_TYPE.pop(_FakeConfig, None)
+
+
+def test_register_user_simulator_overwrites_existing_entry():
+  """Re-registering the same config type must overwrite the previous entry.
+
+  This lets a test or an out-of-tree extension swap in an alternative
+  implementation for the same config type without having to unregister first.
+  """
+
+  class _AlternativeFakeSimulator(UserSimulator):
+    pass
+
+  try:
+    register_user_simulator(_FakeConfig, _FakeSimulator)
+    register_user_simulator(_FakeConfig, _AlternativeFakeSimulator)
+    assert (
+        user_simulator_module._SIMULATOR_BY_CONFIG_TYPE.get(_FakeConfig)
+        is _AlternativeFakeSimulator
+    )
+  finally:
+    user_simulator_module._SIMULATOR_BY_CONFIG_TYPE.pop(_FakeConfig, None)