[Bugfix] Add validation for wrong connection type for LLM node. (#1685)

# Description

Add validation for wrong connection type for LLM node.
This pull request includes changes related to testing and validation of
connections in the `promptflow` codebase. The most important changes
include adding a new test case to validate the behavior when a tool load
fails due to an invalid connection type, and adding a check to validate
the connection type of a node in the `_resolve_llm_node` method.

Testing and validation changes:

* `src/promptflow/tests/executor/e2etests/test_executor_validation.py`:
Added a new test case to validate the behavior when a tool load fails
due to an invalid connection type. (test_executor_validation.py)
* `src/promptflow/promptflow/executor/_tool_resolver.py`: Added a check
to validate the connection type of a node in the `_resolve_llm_node`
method. (src/promptflow/promptflow/executor/_tool_resolver.py)

Additional changes:

*
`src/promptflow/tests/test_configs/wrong_flows/flow_llm_with_wrong_conn/flow.dag.yaml`:
Added a new YAML file that defines a node with a custom connection.
(src/promptflow/tests/test_configs/wrong_flows/flow_llm_with_wrong_conn/flow.dag.yaml)
*
`src/promptflow/tests/test_configs/wrong_flows/flow_llm_with_wrong_conn/wrong_llm.jinja2`:
Added a new Jinja2 template file containing a system message and a user
message that uses a Jinja2 variable.
(src/promptflow/tests/test_configs/wrong_flows/flow_llm_with_wrong_conn/wrong_llm.jinja2)

# All Promptflow Contribution checklist:
- [ ] **The pull request does not introduce [breaking changes].**
- [ ] **CHANGELOG is updated for new features, bug fixes or other
significant changes.**
- [ ] **I have read the [contribution guidelines](../CONTRIBUTING.md).**
- [ ] **Create an issue and link to the pull request to get dedicated
review from promptflow team. Learn more: [suggested
workflow](../CONTRIBUTING.md#suggested-workflow).**

## General Guidelines and Best Practices
- [ ] Title of the pull request is clear and informative.
- [ ] There are a small number of commits, each of which have an
informative message. This means that previously merged commits do not
appear in the history of the PR. For more information on cleaning up the
commits in your PR, [see this
page](https://github.com/Azure/azure-powershell/blob/master/documentation/development-docs/cleaning-up-commits.md).

### Testing Guidelines
- [ ] Pull request includes test coverage for the included changes.

Co-authored-by: Heyi Tang <[email protected]>

src/promptflow/promptflow/executor/_tool_resolver.py

@@ -276,7 +276,13 @@ def _resolve_llm_node(self, node: Node, convert_input_types=False) -> ResolvedTo
             if not connection_type_to_api_mapping:
                 raise EmptyLLMApiMapping()
             # If provider is not specified, try to resolve it from connection type
-            node.provider = connection_type_to_api_mapping.get(type(connection).__name__)
+            connection_type = type(connection).__name__
+            if connection_type not in connection_type_to_api_mapping:
+                raise InvalidConnectionType(
+                    message_format="Connection type {conn_type} is not supported for LLM.",
+                    conn_type=connection_type,
+                )
+            node.provider = connection_type_to_api_mapping[connection_type]
         tool: Tool = self._tool_loader.load_tool_for_llm_node(node)
         key, connection = self._resolve_llm_connection_to_inputs(node, tool)
         updated_node = copy.deepcopy(node)

src/promptflow/tests/executor/e2etests/test_executor_validation.py

@@ -19,6 +19,7 @@
     InputNotFound,
     InputReferenceNotFound,
     InputTypeError,
+    InvalidConnectionType,
     InvalidSource,
     NodeCircularDependency,
     NodeInputValidationError,
@@ -37,6 +38,16 @@ class TestValidation:
     @pytest.mark.parametrize(
         "flow_folder, yml_file, error_class, inner_class, error_msg",
         [
+            (
+                "flow_llm_with_wrong_conn",
+                "flow.dag.yaml",
+                ResolveToolError,
+                InvalidConnectionType,
+                (
+                    "Tool load failed in 'wrong_llm': "
+                    "(InvalidConnectionType) Connection type CustomConnection is not supported for LLM."
+                )
+            ),
             (
                 "nodes_names_duplicated",
                 "flow.dag.yaml",

src/promptflow/tests/test_configs/wrong_flows/flow_llm_with_wrong_conn/flow.dag.yaml

@@ -0,0 +1,10 @@
+inputs: {}
+outputs: {}
+nodes:
+- name: wrong_llm
+  type: llm
+  source:
+    type: code
+    path: wrong_llm.jinja2
+  inputs: {}
+  connection: custom_connection

src/promptflow/tests/test_configs/wrong_flows/flow_llm_with_wrong_conn/wrong_llm.jinja2

@@ -0,0 +1,5 @@
+system:
+You are a helpful assistant.
+
+user:
+{{question}}