fix: improve tool validation error messages and add comprehensive tests

- Fix error message for missing modules to be more descriptive
- Remove redundant 'to properly import this tool' text from error messages
- Add specific error messages for missing modules vs missing functions
- Add unit tests for each error case:
  - Invalid tool (not file/module/@tool)
  - Missing module (module doesn't exist)
  - Missing function (function not found in existing module)
- All 17 tests passing with better error coverage

🤖 Assisted by Amazon Q Developer

Author: mrlee-amazon

src/strands/experimental/agent_config.py

@@ -82,18 +82,18 @@ def _validate_tools(tools: list[str]) -> None:
                     module = importlib.import_module(module_path)
                     if not hasattr(module, func_name):
                         raise ValueError(
-                            f"Tool '{tool}' not found. The configured tool is not annotated with @tool, "
-                            f"and is not a module or file. To properly import this tool, you must annotate it with @tool."
+                            f"Function '{func_name}' not found in module '{module_path}'. "
+                            f"Ensure the function exists and is annotated with @tool."
                         )
                 except ImportError:
                     raise ValueError(
-                        f"Tool '{tool}' not found. The configured tool is not annotated with @tool, "
-                        f"and is not a module or file. To properly import this tool, you must annotate it with @tool."
+                        f"Module '{module_path}' not found. "
+                        f"Ensure the module exists and is importable, or use a valid file path."
                     )
             else:
                 raise ValueError(
-                    f"Tool '{tool}' not found. The configured tool is not annotated with @tool, "
-                    f"and is not a module or file. To properly import this tool, you must annotate it with @tool."
+                    f"Tool '{tool}' not found. "
+                    f"The configured tool is not annotated with @tool, and is not a module or file."
                 )
 
 

tests/strands/experimental/test_agent_config.py

@@ -136,3 +136,15 @@ def test_config_to_agent_validation_error_invalid_tool(self):
         config = {"model": "test-model", "tools": ["nonexistent_tool"]}
         with pytest.raises(ValueError, match="The configured tool is not annotated with @tool"):
             config_to_agent(config)
+
+    def test_config_to_agent_validation_error_missing_module(self):
+        """Test that missing modules raise helpful error messages."""
+        config = {"model": "test-model", "tools": ["nonexistent.module.tool"]}
+        with pytest.raises(ValueError, match="Module 'nonexistent.module' not found"):
+            config_to_agent(config)
+
+    def test_config_to_agent_validation_error_missing_function(self):
+        """Test that missing functions in existing modules raise helpful error messages."""
+        config = {"model": "test-model", "tools": ["json.nonexistent_function"]}
+        with pytest.raises(ValueError, match="Function 'nonexistent_function' not found in module 'json'"):
+            config_to_agent(config)