feat: Adds Static User Simulator and User Simulator Provider

Details:
- Adds the `StaticUserSimulator` which implements the current functionality of supplying a fixed set of user prompts for an EvalCase.
- Adds the `UserSimulatorProvider` which determines the type of user simulator required for an EvalCase (StaticUserSimulator or LlmBackedUserSimulator).
- Integrates the UserSimulatorProvider and UserSimulator into the CLI and evaluation infrastructure.
- Updates and adds unit tests for the new functionality.
- Miscellaneous updates to lay groundwork for a full implementation of the LlmBackedUserSimulator in the future.
PiperOrigin-RevId: 822198401

tests/unittests/evaluation/test_user_simulator_provider.py

@@ -0,0 +1,79 @@
+# Copyright 2025 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 import conversation_scenarios
+from google.adk.evaluation import eval_case
+from google.adk.evaluation import user_simulator_provider
+from google.adk.evaluation.llm_backed_user_simulator import LlmBackedUserSimulator
+from google.adk.evaluation.llm_backed_user_simulator import LlmBackedUserSimulatorConfig
+from google.adk.evaluation.static_user_simulator import StaticUserSimulator
+from google.genai import types
+import pytest
+
+_TEST_CONVERSATION = [
+    eval_case.Invocation(
+        invocation_id='inv1',
+        user_content=types.Content(parts=[types.Part(text='Hello!')]),
+    ),
+]
+
+_TEST_CONVERSATION_SCENARIO = conversation_scenarios.ConversationScenario(
+    starting_prompt='Hello!', conversation_plan='test plan'
+)
+
+
+class TestUserSimulatorProvider:
+  """Test cases for the UserSimulatorProvider."""
+
+  def test_provide_static_user_simulator(self):
+    """Tests the case when a StaticUserSimulator should be provided."""
+    provider = user_simulator_provider.UserSimulatorProvider()
+    test_eval_case = eval_case.EvalCase(
+        eval_id='test_eval_id',
+        conversation=_TEST_CONVERSATION,
+    )
+    simulator = provider.provide(test_eval_case)
+    assert isinstance(simulator, StaticUserSimulator)
+    assert simulator.static_conversation == _TEST_CONVERSATION
+
+  def test_provide_llm_backed_user_simulator(self, mocker):
+    """Tests the case when a LlmBackedUserSimulator should be provided."""
+    mock_llm_registry = mocker.patch(
+        'google.adk.evaluation.llm_backed_user_simulator.LLMRegistry',
+        autospec=True,
+    )
+    mock_llm_registry.return_value.resolve.return_value = mocker.Mock()
+    # Test case 1: No config in provider.
+    provider = user_simulator_provider.UserSimulatorProvider()
+    test_eval_case = eval_case.EvalCase(
+        eval_id='test_eval_id',
+        conversation_scenario=_TEST_CONVERSATION_SCENARIO,
+    )
+    simulator = provider.provide(test_eval_case)
+    assert isinstance(simulator, LlmBackedUserSimulator)
+    assert simulator._conversation_scenario == _TEST_CONVERSATION_SCENARIO
+
+    # Test case 2: Config in provider.
+    llm_config = LlmBackedUserSimulatorConfig(
+        model='test_model',
+    )
+    provider = user_simulator_provider.UserSimulatorProvider(
+        user_simulator_config=llm_config
+    )
+    simulator = provider.provide(test_eval_case)
+    assert isinstance(simulator, LlmBackedUserSimulator)
+    assert simulator._conversation_scenario == _TEST_CONVERSATION_SCENARIO
+    assert simulator._config.model == 'test_model'