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import pytest
import json
from unittest.mock import mock_open, patch
from wperf_cmn_visualizer.topology_loader import cmn_topology_loader


class TestTopologyLoader:
    """Tests for the topology loader functionality."""

    def test_load_valid_json_file(self):
        """Test loading a valid JSON topology file."""
        test_data = {"elements": [{"config": {"X": 2, "Y": 2}}]}
        json_content = json.dumps(test_data)
        # mock open files
        with patch("builtins.open", mock_open(read_data=json_content)):
            loader = cmn_topology_loader()
            loader.load_topology_from_file("test.json")
            assert loader.data == test_data

    def test_load_nonexistent_file(self):
        """Test error handling when file doesn't exist."""
        loader = cmn_topology_loader()
        with pytest.raises(FileNotFoundError):
            loader.load_topology_from_file("nonexistent.json")

    def test_load_invalid_json(self):
        """Test error handling for malformed JSON."""
        invalid_json = '{"elements": [invalid json}'

        with patch("builtins.open", mock_open(read_data=invalid_json)):
            loader = cmn_topology_loader()
            with pytest.raises(ValueError):
                loader.load_topology_from_file("test.json")

    def test_load_empty_file(self):
        """Test error handling for empty JSON file."""
        with patch("builtins.open", mock_open(read_data="")):
            loader = cmn_topology_loader()
            with pytest.raises(ValueError):
                loader.load_topology_from_file("test.json")

    def test_load_null_data(self):
        """Test error handling for null JSON data."""
        with patch("builtins.open", mock_open(read_data="null")):
            loader = cmn_topology_loader()
            with pytest.raises(AssertionError):
                loader.load_topology_from_file("test.json")
