chore: import upstream snapshot with attribution

tests/unittests/agents/test_llm_agent_error_messages.py

@@ -0,0 +1,90 @@
+# 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.
+
+"""Tests for enhanced error messages in agent handling."""
+
+from google.adk.agents.llm_agent import LlmAgent
+import pytest
+
+
+def test_agent_not_found_enhanced_error():
+  """Verify enhanced error message for agent not found."""
+  root_agent = LlmAgent(
+      name='root',
+      model='gemini-2.5-flash',
+      sub_agents=[
+          LlmAgent(name='agent_a', model='gemini-2.5-flash'),
+          LlmAgent(name='agent_b', model='gemini-2.5-flash'),
+      ],
+  )
+
+  with pytest.raises(ValueError) as exc_info:
+    root_agent._LlmAgent__get_agent_to_run('nonexistent_agent')
+
+  error_msg = str(exc_info.value)
+
+  # Verify error message components
+  assert 'nonexistent_agent' in error_msg
+  assert 'Available agents:' in error_msg
+  assert 'agent_a' in error_msg
+  assert 'agent_b' in error_msg
+  assert 'Possible causes:' in error_msg
+  assert 'Suggested fixes:' in error_msg
+
+
+def test_agent_tree_traversal():
+  """Verify agent tree traversal helper works correctly."""
+  root_agent = LlmAgent(
+      name='orchestrator',
+      model='gemini-2.5-flash',
+      sub_agents=[
+          LlmAgent(
+              name='parent_agent',
+              model='gemini-2.5-flash',
+              sub_agents=[
+                  LlmAgent(name='child_agent', model='gemini-2.5-flash'),
+              ],
+          ),
+      ],
+  )
+
+  available_agents = root_agent._get_available_agent_names()
+
+  # Verify all agents in tree are found
+  assert 'orchestrator' in available_agents
+  assert 'parent_agent' in available_agents
+  assert 'child_agent' in available_agents
+  assert len(available_agents) == 3
+
+
+def test_agent_not_found_shows_all_agents():
+  """Verify error message shows all agents (no truncation)."""
+  # Create 100 sub-agents
+  sub_agents = [
+      LlmAgent(name=f'agent_{i}', model='gemini-2.5-flash') for i in range(100)
+  ]
+
+  root_agent = LlmAgent(
+      name='root', model='gemini-2.5-flash', sub_agents=sub_agents
+  )
+
+  with pytest.raises(ValueError) as exc_info:
+    root_agent._LlmAgent__get_agent_to_run('nonexistent')
+
+  error_msg = str(exc_info.value)
+
+  # Verify all agents are shown (no truncation)
+  assert 'agent_0' in error_msg  # First agent shown
+  assert 'agent_99' in error_msg  # Last agent also shown
+  assert 'showing first 20 of' not in error_msg  # No truncation message