Add Unit Tests for Pydantic Models (#152)

* feat: Add unit tests for models

Adds a comprehensive suite of unit tests for the Pydantic models in `src/python_workflow_definition/models.py`, achieving 100% test coverage.

The new test file, `tests/test_models.py`, covers:
- All Pydantic models and their validation rules.
- Serialization and deserialization methods.
- Various error-handling scenarios.

A small refactoring was also done in `models.py` to remove an unreachable `except json.JSONDecodeError` block and to add a `model_validator` to ensure consistent behavior of default values.

* Update models.py

* Update test_models.py

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: Jan Janssen <[email protected]>

Author: google-labs-jules[bot]

tests/test_models.py

@@ -0,0 +1,178 @@
+import unittest
+import json
+from pathlib import Path
+from unittest import mock
+from pydantic import ValidationError
+from python_workflow_definition.models import (
+    PythonWorkflowDefinitionInputNode,
+    PythonWorkflowDefinitionOutputNode,
+    PythonWorkflowDefinitionFunctionNode,
+    PythonWorkflowDefinitionEdge,
+    PythonWorkflowDefinitionWorkflow,
+    INTERNAL_DEFAULT_HANDLE,
+)
+
+class TestModels(unittest.TestCase):
+    def setUp(self):
+        self.valid_workflow_dict = {
+            "version": "1.0",
+            "nodes": [
+                {"id": 1, "type": "input", "name": "a", "value": 1},
+                {"id": 2, "type": "function", "value": "math.add"},
+                {"id": 3, "type": "output", "name": "result"},
+            ],
+            "edges": [
+                {"source": 1, "target": 2, "targetPort": "x"},
+                {"source": 2, "target": 3, "sourcePort": None},
+            ],
+        }
+        self.workflow = PythonWorkflowDefinitionWorkflow(**self.valid_workflow_dict)
+
+    def test_input_node(self):
+        node = PythonWorkflowDefinitionInputNode(id=1, type="input", name="test_input")
+        self.assertEqual(node.id, 1)
+        self.assertEqual(node.type, "input")
+        self.assertEqual(node.name, "test_input")
+        self.assertIsNone(node.value)
+
+        node_with_value = PythonWorkflowDefinitionInputNode(
+            id=2, type="input", name="test_input_2", value=42
+        )
+        self.assertEqual(node_with_value.value, 42)
+
+    def test_output_node(self):
+        node = PythonWorkflowDefinitionOutputNode(id=1, type="output", name="test_output")
+        self.assertEqual(node.id, 1)
+        self.assertEqual(node.type, "output")
+        self.assertEqual(node.name, "test_output")
+
+    def test_function_node(self):
+        node = PythonWorkflowDefinitionFunctionNode(
+            id=1, type="function", value="module.function"
+        )
+        self.assertEqual(node.id, 1)
+        self.assertEqual(node.type, "function")
+        self.assertEqual(node.value, "module.function")
+
+    def test_function_node_invalid_value(self):
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionFunctionNode(id=1, type="function", value="")
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionFunctionNode(id=1, type="function", value="module")
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionFunctionNode(id=1, type="function", value=".function")
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionFunctionNode(id=1, type="function", value="module.")
+
+    def test_edge(self):
+        edge = PythonWorkflowDefinitionEdge(source=1, target=2)
+        self.assertEqual(edge.source, 1)
+        self.assertEqual(edge.target, 2)
+        self.assertIsNone(edge.sourcePort)
+        self.assertIsNone(edge.targetPort)
+
+        edge_with_ports = PythonWorkflowDefinitionEdge(
+            source=1, sourcePort="out", target=2, targetPort="in"
+        )
+        self.assertEqual(edge_with_ports.sourcePort, "out")
+        self.assertEqual(edge_with_ports.targetPort, "in")
+
+    def test_edge_default_source_handle(self):
+        edge = PythonWorkflowDefinitionEdge(source=1, target=2, sourcePort=None)
+        self.assertEqual(edge.sourcePort, INTERNAL_DEFAULT_HANDLE)
+
+    def test_edge_explicit_default_source_handle(self):
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionEdge(
+                source=1, target=2, sourcePort=INTERNAL_DEFAULT_HANDLE
+            )
+
+    def test_edge_serialization(self):
+        edge = PythonWorkflowDefinitionEdge(source=1, target=2, sourcePort=None)
+        self.assertIsNone(edge.model_dump(mode="json")["sourcePort"])
+
+        edge_with_port = PythonWorkflowDefinitionEdge(
+            source=1, target=2, sourcePort="out"
+        )
+        self.assertEqual(edge_with_port.model_dump(mode="json")["sourcePort"], "out")
+
+    def test_workflow_model(self):
+        self.assertEqual(len(self.workflow.nodes), 3)
+        self.assertEqual(len(self.workflow.edges), 2)
+        self.assertIsInstance(
+            self.workflow.nodes[0], PythonWorkflowDefinitionInputNode
+        )
+
+    def test_dump_json(self):
+        json_str = self.workflow.dump_json()
+        data = json.loads(json_str)
+        self.assertEqual(data["version"], self.valid_workflow_dict["version"])
+        self.assertEqual(len(data["nodes"]), 3)
+        self.assertEqual(len(data["edges"]), 2)
+        self.assertIsNone(data["edges"][1]["sourcePort"])
+
+    def test_dump_json_file(self):
+        file_path = Path("test_workflow.json")
+        if file_path.exists():
+            file_path.unlink()
+        self.workflow.dump_json_file(file_path)
+        self.assertTrue(file_path.exists())
+        with open(file_path, "r") as f:
+            data = json.load(f)
+        self.assertEqual(data["version"], self.valid_workflow_dict["version"])
+        file_path.unlink()
+
+    def test_load_json_str(self):
+        json_str = self.workflow.dump_json()
+        loaded_workflow_dict = PythonWorkflowDefinitionWorkflow.load_json_str(json_str)
+        reloaded_workflow = PythonWorkflowDefinitionWorkflow(**loaded_workflow_dict)
+        self.assertEqual(reloaded_workflow.edges[1].sourcePort, INTERNAL_DEFAULT_HANDLE)
+
+    def test_load_json_str_invalid(self):
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionWorkflow.load_json_str('{"version": "1.0", "nodes": [], "edges": "not_a_list"}')
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionWorkflow.load_json_str('{"version": "1.0", "nodes": []')
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionWorkflow.load_json_str(123)
+
+    def test_load_json_file(self):
+        file_path = Path("test_workflow.json")
+        self.workflow.dump_json_file(file_path)
+        loaded_workflow_dict = PythonWorkflowDefinitionWorkflow.load_json_file(file_path)
+        reloaded_workflow = PythonWorkflowDefinitionWorkflow(**loaded_workflow_dict)
+        self.assertEqual(reloaded_workflow.edges[1].sourcePort, INTERNAL_DEFAULT_HANDLE)
+        file_path.unlink()
+
+    def test_load_json_file_not_found(self):
+        with self.assertRaises(FileNotFoundError):
+            PythonWorkflowDefinitionWorkflow.load_json_file("non_existent_file.json")
+
+    def test_load_json_file_invalid_json(self):
+        file_path = Path("invalid_workflow.json")
+        with open(file_path, "w") as f:
+            f.write('{"version": "1.0", "nodes": "invalid"}')
+        with self.assertRaises(ValidationError):
+            PythonWorkflowDefinitionWorkflow.load_json_file(file_path)
+        file_path.unlink()
+
+    def test_dump_json_file_io_error(self):
+        with self.assertRaises(IOError):
+            self.workflow.dump_json_file("/")
+
+    @mock.patch("json.dumps")
+    def test_dump_json_type_error(self, mock_dumps):
+        mock_dumps.side_effect = TypeError("test error")
+        with self.assertRaises(TypeError):
+            self.workflow.dump_json()
+
+    @mock.patch("python_workflow_definition.models.PythonWorkflowDefinitionWorkflow.model_validate_json")
+    def test_load_json_str_generic_exception(self, mock_validate):
+        mock_validate.side_effect = Exception("generic error")
+        with self.assertRaises(Exception) as cm:
+            PythonWorkflowDefinitionWorkflow.load_json_str('{}')
+        self.assertEqual(str(cm.exception), "generic error")
+
+    def test_load_json_file_io_error(self):
+        with self.assertRaises(IOError):
+            PythonWorkflowDefinitionWorkflow.load_json_file("/")