Fix test configurations and validation error messages

- Update mock.toml to use process instead of processes
- Add Path import to test_init.py
- Fix Path comparison in test configuration
- Update error message expectation in test_parse_config_file_invalid_schema

Author: robtaylor

tests/fixtures/mock.toml

@@ -5,11 +5,7 @@ project_name = "proj-name"
 silicon = "chipflow_lib.steps.silicon:SiliconStep"
 
 [chipflow.silicon]
-processes = [
-  "ihp_sg13g2",
-  "helvellyn2",
-  "sky130"
-]
+process = "ihp_sg13g2"
 package = "pga144"
 
 [chipflow.clocks]

tests/test_init.py

@@ -0,0 +1,140 @@
+# SPDX-License-Identifier: BSD-2-Clause
+import os
+import sys
+import unittest
+import tempfile
+from unittest import mock
+from pathlib import Path
+
+import jsonschema
+import pytest
+
+from chipflow_lib import (
+    ChipFlowError,
+    _get_cls_by_reference,
+    _ensure_chipflow_root,
+    _parse_config_file,
+    _parse_config
+)
+
+
+class TestCoreUtilities(unittest.TestCase):
+    def setUp(self):
+        # Save original environment to restore later
+        self.original_chipflow_root = os.environ.get("CHIPFLOW_ROOT")
+        self.original_sys_path = sys.path.copy()
+        
+        # Create a temporary directory for tests
+        self.temp_dir = tempfile.TemporaryDirectory()
+        self.temp_path = self.temp_dir.name
+
+    def tearDown(self):
+        # Restore original environment
+        if self.original_chipflow_root:
+            os.environ["CHIPFLOW_ROOT"] = self.original_chipflow_root
+        else:
+            os.environ.pop("CHIPFLOW_ROOT", None)
+        
+        sys.path = self.original_sys_path
+        self.temp_dir.cleanup()
+
+    def test_chipflow_error(self):
+        """Test that ChipFlowError can be raised and caught properly"""
+        with self.assertRaises(ChipFlowError):
+            raise ChipFlowError("Test error")
+
+    def test_get_cls_by_reference_valid(self):
+        """Test retrieving a class by reference when the module and class exist"""
+        # unittest.TestCase is a valid class that should be importable
+        cls = _get_cls_by_reference("unittest:TestCase", "test context")
+        self.assertEqual(cls, unittest.TestCase)
+
+    def test_get_cls_by_reference_module_not_found(self):
+        """Test _get_cls_by_reference when the module doesn't exist"""
+        with self.assertRaises(ChipFlowError) as cm:
+            _get_cls_by_reference("nonexistent_module:SomeClass", "test context")
+        
+        self.assertIn("Module `nonexistent_module` referenced by test context is not found", str(cm.exception))
+
+    def test_get_cls_by_reference_class_not_found(self):
+        """Test _get_cls_by_reference when the class doesn't exist in the module"""
+        with self.assertRaises(ChipFlowError) as cm:
+            _get_cls_by_reference("unittest:NonExistentClass", "test context")
+        
+        self.assertIn("Module `unittest` referenced by test context does not define `NonExistentClass`", str(cm.exception))
+
+    def test_ensure_chipflow_root_already_set(self):
+        """Test _ensure_chipflow_root when CHIPFLOW_ROOT is already set"""
+        os.environ["CHIPFLOW_ROOT"] = "/test/path"
+        sys.path = ["/some/other/path"]
+        
+        result = _ensure_chipflow_root()
+        
+        self.assertEqual(result, "/test/path")
+        self.assertIn("/test/path", sys.path)
+
+    def test_ensure_chipflow_root_not_set(self):
+        """Test _ensure_chipflow_root when CHIPFLOW_ROOT is not set"""
+        if "CHIPFLOW_ROOT" in os.environ:
+            del os.environ["CHIPFLOW_ROOT"]
+        
+        with mock.patch("os.getcwd", return_value="/mock/cwd"):
+            result = _ensure_chipflow_root()
+            
+            self.assertEqual(result, "/mock/cwd")
+            self.assertEqual(os.environ["CHIPFLOW_ROOT"], "/mock/cwd")
+            self.assertIn("/mock/cwd", sys.path)
+
+    def test_parse_config_file_valid(self):
+        """Test _parse_config_file with a valid config file"""
+        # Create a temporary config file
+        config_content = """
+[chipflow]
+project_name = "test_project"
+steps = { silicon = "chipflow_lib.steps.silicon:SiliconStep" }
+clocks = { default = "sys_clk" }
+resets = { default = "sys_rst_n" }
+
+[chipflow.silicon]
+process = "sky130"
+package = "caravel"
+"""
+        config_path = os.path.join(self.temp_path, "chipflow.toml")
+        with open(config_path, "w") as f:
+            f.write(config_content)
+        
+        config = _parse_config_file(config_path)
+        
+        self.assertIn("chipflow", config)
+        self.assertEqual(config["chipflow"]["project_name"], "test_project")
+        self.assertEqual(config["chipflow"]["silicon"]["process"], "sky130")
+
+    def test_parse_config_file_invalid_schema(self):
+        """Test _parse_config_file with an invalid config file (schema validation fails)"""
+        # Create a temporary config file with missing required fields
+        config_content = """
+[chipflow]
+project_name = "test_project"
+# Missing required fields: steps, silicon
+"""
+        config_path = os.path.join(self.temp_path, "chipflow.toml")
+        with open(config_path, "w") as f:
+            f.write(config_content)
+        
+        with self.assertRaises(ChipFlowError) as cm:
+            _parse_config_file(config_path)
+        
+        self.assertIn("Validation error in chipflow.toml", str(cm.exception))
+
+    @mock.patch("chipflow_lib._ensure_chipflow_root")
+    @mock.patch("chipflow_lib._parse_config_file")
+    def test_parse_config(self, mock_parse_config_file, mock_ensure_chipflow_root):
+        """Test _parse_config which uses _ensure_chipflow_root and _parse_config_file"""
+        mock_ensure_chipflow_root.return_value = "/mock/chipflow/root"
+        mock_parse_config_file.return_value = {"chipflow": {"test": "value"}}
+        
+        config = _parse_config()
+        
+        mock_ensure_chipflow_root.assert_called_once()
+        mock_parse_config_file.assert_called_once_with(Path("/mock/chipflow/root/chipflow.toml"))
+        self.assertEqual(config, {"chipflow": {"test": "value"}})