feat: restructure as monorepo

- Move core CrewAI to packages/crewai with git mv to preserve history
- Create workspace-level pyproject.toml with uv workspace configuration
- Rename core package to crewai-core
- Setup workspace sources for internal package dependencies

packages/crewai/tests/utilities/test_import_utils.py

@@ -0,0 +1,42 @@
+"""Tests for import utilities."""
+
+import pytest
+from unittest.mock import patch
+
+from crewai.utilities.import_utils import require, OptionalDependencyError
+
+
+class TestRequire:
+    """Test the require function."""
+
+    def test_require_existing_module(self):
+        """Test requiring a module that exists."""
+        module = require("json", purpose="testing")
+        assert module.__name__ == "json"
+
+    def test_require_missing_module(self):
+        """Test requiring a module that doesn't exist."""
+        with pytest.raises(OptionalDependencyError) as exc_info:
+            require("nonexistent_module_xyz", purpose="testing missing module")
+
+        error_msg = str(exc_info.value)
+        assert (
+            "testing missing module requires the optional dependency 'nonexistent_module_xyz'"
+            in error_msg
+        )
+        assert "uv add nonexistent_module_xyz" in error_msg
+
+    def test_require_with_import_error(self):
+        """Test that ImportError is properly chained."""
+        with patch("importlib.import_module") as mock_import:
+            mock_import.side_effect = ImportError("Module import failed")
+
+            with pytest.raises(OptionalDependencyError) as exc_info:
+                require("some_module", purpose="testing error handling")
+
+            assert isinstance(exc_info.value.__cause__, ImportError)
+            assert str(exc_info.value.__cause__) == "Module import failed"
+
+    def test_optional_dependency_error_is_import_error(self):
+        """Test that OptionalDependencyError is a subclass of ImportError."""
+        assert issubclass(OptionalDependencyError, ImportError)