From 00519320146c795f1c320ce7e6c1898570a89bdc Mon Sep 17 00:00:00 2001
From: phg <mail@philip-henning.com>
Date: Tue, 29 Jul 2025 21:14:29 +0200
Subject: [PATCH] Add comprehensive tests for configuration management and main
 TUI components

---
 memory-bank/progress.md    |   4 +-
 tests/test_config.py       | 292 ++++++++++++++++++++++
 tests/test_config_modal.py | 229 ++++++++++++++++++
 tests/test_main.py         | 484 +++++++++++++++++++++++++++++++++++++
 4 files changed, 1008 insertions(+), 1 deletion(-)
 create mode 100644 tests/test_config.py
 create mode 100644 tests/test_config_modal.py
 create mode 100644 tests/test_main.py

diff --git a/memory-bank/progress.md b/memory-bank/progress.md
index 2823609..28b367c 100644
--- a/memory-bank/progress.md
+++ b/memory-bank/progress.md
@@ -19,7 +19,7 @@
 - ✅ **Entry management**: List view with proper formatting and status indicators
 - ✅ **Detail view**: Comprehensive entry details in right pane
 - ✅ **Navigation**: Smooth keyboard navigation with cursor position restoration
-- ✅ **Testing**: 42 comprehensive tests with 100% pass rate
+- ✅ **Testing**: 97 comprehensive tests with 100% pass rate
 - ✅ **Code quality**: All ruff linting and formatting checks passing
 - ✅ **Error handling**: Graceful handling of file access and parsing errors
 - ✅ **Status feedback**: Informative status bar with file and entry information
@@ -100,6 +100,8 @@
 - ✅ **File integrity**: Perfect preservation of comments and formatting
 - ✅ **Test coverage**: Comprehensive test suite catching all edge cases
 - ✅ **Development workflow**: Smooth uv-based development experience
+- ✅ **Complete test implementation**: Added comprehensive tests for config and main TUI components
+- ✅ **Test-driven development**: All 97 tests passing with full coverage of application functionality
 
 ## Technical Implementation Details
 
diff --git a/tests/test_config.py b/tests/test_config.py
new file mode 100644
index 0000000..bc4a86a
--- /dev/null
+++ b/tests/test_config.py
@@ -0,0 +1,292 @@
+"""
+Tests for the configuration management module.
+
+This module contains unit tests for the Config class,
+validating configuration loading, saving, and management functionality.
+"""
+
+import pytest
+import tempfile
+import json
+import os
+from pathlib import Path
+from unittest.mock import patch, mock_open
+
+from hosts.core.config import Config
+
+
+class TestConfig:
+    """Test cases for the Config class."""
+    
+    def test_config_initialization(self):
+        """Test basic config initialization with defaults."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            # Check default settings
+            assert config.get("show_default_entries") is False
+            assert len(config.get("default_entries", [])) == 3
+            assert config.get("window_settings", {}).get("last_sort_column") == ""
+            assert config.get("window_settings", {}).get("last_sort_ascending") is True
+    
+    def test_default_settings_structure(self):
+        """Test that default settings have the expected structure."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            default_entries = config.get("default_entries", [])
+            assert len(default_entries) == 3
+            
+            # Check localhost entries
+            localhost_entries = [e for e in default_entries if e["hostname"] == "localhost"]
+            assert len(localhost_entries) == 2  # IPv4 and IPv6
+            
+            # Check broadcasthost entry
+            broadcast_entries = [e for e in default_entries if e["hostname"] == "broadcasthost"]
+            assert len(broadcast_entries) == 1
+            assert broadcast_entries[0]["ip"] == "255.255.255.255"
+    
+    def test_config_paths(self):
+        """Test that config paths are set correctly."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            expected_dir = Path.home() / ".config" / "hosts-manager"
+            expected_file = expected_dir / "config.json"
+            
+            assert config.config_dir == expected_dir
+            assert config.config_file == expected_file
+    
+    def test_get_existing_key(self):
+        """Test getting an existing configuration key."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            result = config.get("show_default_entries")
+            assert result is False
+    
+    def test_get_nonexistent_key_with_default(self):
+        """Test getting a nonexistent key with default value."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            result = config.get("nonexistent_key", "default_value")
+            assert result == "default_value"
+    
+    def test_get_nonexistent_key_without_default(self):
+        """Test getting a nonexistent key without default value."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            result = config.get("nonexistent_key")
+            assert result is None
+    
+    def test_set_configuration_value(self):
+        """Test setting a configuration value."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            config.set("test_key", "test_value")
+            assert config.get("test_key") == "test_value"
+    
+    def test_set_overwrites_existing_value(self):
+        """Test that setting overwrites existing values."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            # Set initial value
+            config.set("show_default_entries", True)
+            assert config.get("show_default_entries") is True
+            
+            # Overwrite with new value
+            config.set("show_default_entries", False)
+            assert config.get("show_default_entries") is False
+    
+    def test_is_default_entry_true(self):
+        """Test identifying default entries correctly."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            # Test localhost IPv4
+            assert config.is_default_entry("127.0.0.1", "localhost") is True
+            
+            # Test localhost IPv6
+            assert config.is_default_entry("::1", "localhost") is True
+            
+            # Test broadcasthost
+            assert config.is_default_entry("255.255.255.255", "broadcasthost") is True
+    
+    def test_is_default_entry_false(self):
+        """Test that non-default entries are not identified as default."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            # Test custom entries
+            assert config.is_default_entry("192.168.1.1", "router") is False
+            assert config.is_default_entry("10.0.0.1", "test.local") is False
+            assert config.is_default_entry("127.0.0.1", "custom") is False
+    
+    def test_should_show_default_entries_default(self):
+        """Test default value for show_default_entries."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            
+            assert config.should_show_default_entries() is False
+    
+    def test_should_show_default_entries_configured(self):
+        """Test configured value for show_default_entries."""
+        with patch.object(Config, 'load'):
+            config = Config()
+            config.set("show_default_entries", True)
+            
+            assert config.should_show_default_entries() is True
+    
+    def test_toggle_show_default_entries(self):
+        """Test toggling the show_default_entries setting."""
+        with patch.object(Config, 'load'), patch.object(Config, 'save') as mock_save:
+            config = Config()
+            
+            # Initial state should be False
+            assert config.should_show_default_entries() is False
+            
+            # Toggle to True
+            config.toggle_show_default_entries()
+            assert config.should_show_default_entries() is True
+            mock_save.assert_called_once()
+            
+            # Toggle back to False
+            mock_save.reset_mock()
+            config.toggle_show_default_entries()
+            assert config.should_show_default_entries() is False
+            mock_save.assert_called_once()
+    
+    def test_load_nonexistent_file(self):
+        """Test loading config when file doesn't exist."""
+        with patch('pathlib.Path.exists', return_value=False):
+            config = Config()
+            
+            # Should use defaults when file doesn't exist
+            assert config.get("show_default_entries") is False
+    
+    def test_load_existing_file(self):
+        """Test loading config from existing file."""
+        test_config = {
+            "show_default_entries": True,
+            "custom_setting": "custom_value"
+        }
+        
+        with patch('pathlib.Path.exists', return_value=True), \
+             patch('builtins.open', mock_open(read_data=json.dumps(test_config))):
+            config = Config()
+            
+            # Should load values from file
+            assert config.get("show_default_entries") is True
+            assert config.get("custom_setting") == "custom_value"
+            
+            # Should still have defaults for missing keys
+            assert len(config.get("default_entries", [])) == 3
+    
+    def test_load_invalid_json(self):
+        """Test loading config with invalid JSON falls back to defaults."""
+        with patch('pathlib.Path.exists', return_value=True), \
+             patch('builtins.open', mock_open(read_data="invalid json")):
+            config = Config()
+            
+            # Should use defaults when JSON is invalid
+            assert config.get("show_default_entries") is False
+    
+    def test_load_file_io_error(self):
+        """Test loading config with file I/O error falls back to defaults."""
+        with patch('pathlib.Path.exists', return_value=True), \
+             patch('builtins.open', side_effect=IOError("File error")):
+            config = Config()
+            
+            # Should use defaults when file can't be read
+            assert config.get("show_default_entries") is False
+    
+    def test_save_creates_directory(self):
+        """Test that save creates config directory if it doesn't exist."""
+        with patch.object(Config, 'load'), \
+             patch('pathlib.Path.mkdir') as mock_mkdir, \
+             patch('builtins.open', mock_open()) as mock_file:
+            config = Config()
+            config.save()
+            
+            # Should create directory with parents=True, exist_ok=True
+            mock_mkdir.assert_called_once_with(parents=True, exist_ok=True)
+            mock_file.assert_called_once()
+    
+    def test_save_writes_json(self):
+        """Test that save writes configuration as JSON."""
+        with patch.object(Config, 'load'), \
+             patch('pathlib.Path.mkdir'), \
+             patch('builtins.open', mock_open()) as mock_file:
+            config = Config()
+            config.set("test_key", "test_value")
+            config.save()
+            
+            # Check that file was opened for writing
+            mock_file.assert_called_once_with(config.config_file, 'w')
+            
+            # Check that JSON was written
+            handle = mock_file()
+            written_data = ''.join(call.args[0] for call in handle.write.call_args_list)
+            
+            # Should be valid JSON containing our test data
+            parsed_data = json.loads(written_data)
+            assert parsed_data["test_key"] == "test_value"
+    
+    def test_save_io_error_silent_fail(self):
+        """Test that save silently fails on I/O error."""
+        with patch.object(Config, 'load'), \
+             patch('pathlib.Path.mkdir'), \
+             patch('builtins.open', side_effect=IOError("Write error")):
+            config = Config()
+            
+            # Should not raise exception
+            config.save()
+    
+    def test_save_directory_creation_error_silent_fail(self):
+        """Test that save silently fails on directory creation error."""
+        with patch.object(Config, 'load'), \
+             patch('pathlib.Path.mkdir', side_effect=OSError("Permission denied")):
+            config = Config()
+            
+            # Should not raise exception
+            config.save()
+    
+    def test_integration_load_save_roundtrip(self):
+        """Test complete load/save cycle with temporary file."""
+        with tempfile.TemporaryDirectory() as temp_dir:
+            config_dir = Path(temp_dir) / "hosts-manager"
+            config_file = config_dir / "config.json"
+            
+            with patch.object(Config, '__init__', lambda self: None):
+                config = Config()
+                config.config_dir = config_dir
+                config.config_file = config_file
+                config._settings = config._load_default_settings()
+                
+                # Modify some settings
+                config.set("show_default_entries", True)
+                config.set("custom_setting", "test_value")
+                
+                # Save configuration
+                config.save()
+                
+                # Verify file was created
+                assert config_file.exists()
+                
+                # Create new config instance and load
+                config2 = Config()
+                config2.config_dir = config_dir
+                config2.config_file = config_file
+                config2._settings = config2._load_default_settings()
+                config2.load()
+                
+                # Verify settings were loaded correctly
+                assert config2.get("show_default_entries") is True
+                assert config2.get("custom_setting") == "test_value"
+                
+                # Verify defaults are still present
+                assert len(config2.get("default_entries", [])) == 3
diff --git a/tests/test_config_modal.py b/tests/test_config_modal.py
new file mode 100644
index 0000000..7d2bbbf
--- /dev/null
+++ b/tests/test_config_modal.py
@@ -0,0 +1,229 @@
+"""
+Tests for the configuration modal TUI component.
+
+This module contains unit tests for the ConfigModal class,
+validating modal behavior and configuration interaction.
+"""
+
+import pytest
+from unittest.mock import Mock, patch
+
+from textual.widgets import Checkbox, Button
+
+from hosts.core.config import Config
+from hosts.tui.config_modal import ConfigModal
+
+
+class TestConfigModal:
+    """Test cases for the ConfigModal class."""
+    
+    def test_modal_initialization(self):
+        """Test modal initialization with config."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = False
+        
+        modal = ConfigModal(mock_config)
+        assert modal.config == mock_config
+    
+    def test_modal_compose_method_exists(self):
+        """Test that modal has compose method."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = True
+        
+        modal = ConfigModal(mock_config)
+        
+        # Test that compose method exists and is callable
+        assert hasattr(modal, 'compose')
+        assert callable(modal.compose)
+    
+    def test_action_save_updates_config(self):
+        """Test that save action updates configuration."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = False
+        
+        modal = ConfigModal(mock_config)
+        modal.dismiss = Mock()
+        
+        # Mock the checkbox query
+        mock_checkbox = Mock()
+        mock_checkbox.value = True
+        modal.query_one = Mock(return_value=mock_checkbox)
+        
+        # Trigger save action
+        modal.action_save()
+        
+        # Verify config was updated
+        mock_config.set.assert_called_once_with("show_default_entries", True)
+        mock_config.save.assert_called_once()
+        modal.dismiss.assert_called_once_with(True)
+    
+    def test_action_save_preserves_false_state(self):
+        """Test that save action preserves False checkbox state."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = True
+        
+        modal = ConfigModal(mock_config)
+        modal.dismiss = Mock()
+        
+        # Mock the checkbox query with False value
+        mock_checkbox = Mock()
+        mock_checkbox.value = False
+        modal.query_one = Mock(return_value=mock_checkbox)
+        
+        # Trigger save action
+        modal.action_save()
+        
+        # Verify the False value was saved
+        mock_config.set.assert_called_once_with("show_default_entries", False)
+        mock_config.save.assert_called_once()
+        modal.dismiss.assert_called_once_with(True)
+    
+    def test_action_cancel_no_config_changes(self):
+        """Test that cancel action doesn't modify configuration."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = False
+        
+        modal = ConfigModal(mock_config)
+        modal.dismiss = Mock()
+        
+        # Trigger cancel action
+        modal.action_cancel()
+        
+        # Verify config was NOT updated
+        mock_config.set.assert_not_called()
+        mock_config.save.assert_not_called()
+        modal.dismiss.assert_called_once_with(False)
+    
+    def test_save_button_pressed_event(self):
+        """Test save button pressed event handling."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = False
+        
+        modal = ConfigModal(mock_config)
+        modal.action_save = Mock()
+        
+        # Create mock save button
+        save_button = Mock()
+        save_button.id = "save-button"
+        event = Button.Pressed(save_button)
+        
+        modal.on_button_pressed(event)
+        
+        modal.action_save.assert_called_once()
+    
+    def test_cancel_button_pressed_event(self):
+        """Test cancel button pressed event handling."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = False
+        
+        modal = ConfigModal(mock_config)
+        modal.action_cancel = Mock()
+        
+        # Create mock cancel button
+        cancel_button = Mock()
+        cancel_button.id = "cancel-button"
+        event = Button.Pressed(cancel_button)
+        
+        modal.on_button_pressed(event)
+        
+        modal.action_cancel.assert_called_once()
+    
+    def test_unknown_button_pressed_ignored(self):
+        """Test that unknown button presses are ignored."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = False
+        
+        modal = ConfigModal(mock_config)
+        modal.action_save = Mock()
+        modal.action_cancel = Mock()
+        
+        # Create a mock button with unknown ID
+        unknown_button = Mock()
+        unknown_button.id = "unknown-button"
+        event = Button.Pressed(unknown_button)
+        
+        # Should not raise exception
+        modal.on_button_pressed(event)
+        
+        # Should not trigger any actions
+        modal.action_save.assert_not_called()
+        modal.action_cancel.assert_not_called()
+    
+    def test_modal_bindings_defined(self):
+        """Test that modal has expected key bindings."""
+        mock_config = Mock(spec=Config)
+        modal = ConfigModal(mock_config)
+        
+        # Check that bindings are defined
+        assert len(modal.BINDINGS) == 2
+        
+        # Check specific bindings
+        binding_keys = [binding.key for binding in modal.BINDINGS]
+        assert "escape" in binding_keys
+        assert "enter" in binding_keys
+        
+        binding_actions = [binding.action for binding in modal.BINDINGS]
+        assert "cancel" in binding_actions
+        assert "save" in binding_actions
+    
+    def test_modal_css_defined(self):
+        """Test that modal has CSS styling defined."""
+        mock_config = Mock(spec=Config)
+        modal = ConfigModal(mock_config)
+        
+        # Check that CSS is defined
+        assert hasattr(modal, 'CSS')
+        assert isinstance(modal.CSS, str)
+        assert len(modal.CSS) > 0
+        
+        # Check for key CSS classes
+        assert "config-container" in modal.CSS
+        assert "config-title" in modal.CSS
+        assert "button-row" in modal.CSS
+    
+    def test_config_method_called_during_initialization(self):
+        """Test that config method is called during modal setup."""
+        mock_config = Mock(spec=Config)
+        
+        # Test with True
+        mock_config.should_show_default_entries.return_value = True
+        modal = ConfigModal(mock_config)
+        
+        # Verify the config object is stored
+        assert modal.config == mock_config
+        
+        # Test with False
+        mock_config.should_show_default_entries.return_value = False
+        modal = ConfigModal(mock_config)
+        
+        # Verify the config object is stored
+        assert modal.config == mock_config
+    
+    def test_compose_method_signature(self):
+        """Test that compose method has the expected signature."""
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = False
+        
+        modal = ConfigModal(mock_config)
+        
+        # Test that compose method exists and has correct signature
+        import inspect
+        sig = inspect.signature(modal.compose)
+        assert len(sig.parameters) == 0  # No parameters except self
+        
+        # Test return type annotation if present
+        if sig.return_annotation != inspect.Signature.empty:
+            from textual.app import ComposeResult
+            assert sig.return_annotation == ComposeResult
+    
+    def test_modal_inheritance(self):
+        """Test that ConfigModal properly inherits from ModalScreen."""
+        mock_config = Mock(spec=Config)
+        modal = ConfigModal(mock_config)
+        
+        from textual.screen import ModalScreen
+        assert isinstance(modal, ModalScreen)
+        
+        # Should have the config attribute
+        assert hasattr(modal, 'config')
+        assert modal.config == mock_config
diff --git a/tests/test_main.py b/tests/test_main.py
new file mode 100644
index 0000000..6c51846
--- /dev/null
+++ b/tests/test_main.py
@@ -0,0 +1,484 @@
+"""
+Tests for the main TUI application.
+
+This module contains unit tests for the HostsManagerApp class,
+validating application behavior, navigation, and user interactions.
+"""
+
+import pytest
+import tempfile
+from unittest.mock import Mock, patch, MagicMock
+from pathlib import Path
+
+from textual.widgets import DataTable, Static
+
+from hosts.main import HostsManagerApp
+from hosts.core.models import HostEntry, HostsFile
+from hosts.core.parser import HostsParser
+from hosts.core.config import Config
+
+
+class TestHostsManagerApp:
+    """Test cases for the HostsManagerApp class."""
+    
+    def test_app_initialization(self):
+        """Test application initialization."""
+        with patch('hosts.main.HostsParser'), patch('hosts.main.Config'):
+            app = HostsManagerApp()
+            
+            assert app.title == "Hosts Manager"
+            assert app.sub_title == "Read-only mode"
+            assert app.edit_mode is False
+            assert app.selected_entry_index == 0
+            assert app.sort_column == ""
+            assert app.sort_ascending is True
+    
+    def test_app_compose_method_exists(self):
+        """Test that app has compose method."""
+        with patch('hosts.main.HostsParser'), patch('hosts.main.Config'):
+            app = HostsManagerApp()
+            
+            # Test that compose method exists and is callable
+            assert hasattr(app, 'compose')
+            assert callable(app.compose)
+    
+    def test_load_hosts_file_success(self):
+        """Test successful hosts file loading."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        # Create test hosts file
+        test_hosts = HostsFile()
+        test_entry = HostEntry(ip_address="127.0.0.1", hostnames=["localhost"])
+        test_hosts.add_entry(test_entry)
+        
+        mock_parser.parse.return_value = test_hosts
+        mock_parser.get_file_info.return_value = {
+            'path': '/etc/hosts',
+            'exists': True,
+            'size': 100
+        }
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.populate_entries_table = Mock()
+            app.update_entry_details = Mock()
+            app.set_timer = Mock()
+            
+            app.load_hosts_file()
+            
+            # Verify hosts file was loaded
+            assert len(app.hosts_file.entries) == 1
+            assert app.hosts_file.entries[0].ip_address == "127.0.0.1"
+            mock_parser.parse.assert_called_once()
+    
+    def test_load_hosts_file_not_found(self):
+        """Test handling of missing hosts file."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        mock_parser.parse.side_effect = FileNotFoundError("File not found")
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.update_status = Mock()
+            
+            app.load_hosts_file()
+            
+            # Should handle error gracefully
+            app.update_status.assert_called_with("Error: Hosts file not found")
+    
+    def test_load_hosts_file_permission_error(self):
+        """Test handling of permission denied error."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        mock_parser.parse.side_effect = PermissionError("Permission denied")
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.update_status = Mock()
+            
+            app.load_hosts_file()
+            
+            # Should handle error gracefully
+            app.update_status.assert_called_with("Error: Permission denied")
+    
+    def test_populate_entries_table_logic(self):
+        """Test populating DataTable logic without UI dependencies."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        mock_config.should_show_default_entries.return_value = True
+        mock_config.is_default_entry.return_value = False
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Mock the query_one method to return a mock table
+            mock_table = Mock()
+            app.query_one = Mock(return_value=mock_table)
+            
+            # Add test entries
+            app.hosts_file = HostsFile()
+            active_entry = HostEntry(ip_address="127.0.0.1", hostnames=["localhost"])
+            inactive_entry = HostEntry(
+                ip_address="192.168.1.1", 
+                hostnames=["router"], 
+                is_active=False
+            )
+            app.hosts_file.add_entry(active_entry)
+            app.hosts_file.add_entry(inactive_entry)
+            
+            app.populate_entries_table()
+            
+            # Verify table methods were called
+            mock_table.clear.assert_called_once_with(columns=True)
+            mock_table.add_columns.assert_called_once()
+            assert mock_table.add_row.call_count == 2  # Two entries added
+    
+    def test_update_entry_details_with_entry(self):
+        """Test updating entry details pane."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Mock the query_one method
+            mock_details = Mock()
+            app.query_one = Mock(return_value=mock_details)
+            
+            # Add test entry
+            app.hosts_file = HostsFile()
+            test_entry = HostEntry(
+                ip_address="127.0.0.1",
+                hostnames=["localhost", "local"],
+                comment="Test comment"
+            )
+            app.hosts_file.add_entry(test_entry)
+            app.selected_entry_index = 0
+            
+            app.update_entry_details()
+            
+            # Verify update was called with content containing entry details
+            mock_details.update.assert_called_once()
+            call_args = mock_details.update.call_args[0][0]
+            assert "127.0.0.1" in call_args
+            assert "localhost, local" in call_args
+            assert "Test comment" in call_args
+    
+    def test_update_entry_details_no_entries(self):
+        """Test updating entry details with no entries."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Mock the query_one method
+            mock_details = Mock()
+            app.query_one = Mock(return_value=mock_details)
+            
+            app.hosts_file = HostsFile()
+            
+            app.update_entry_details()
+            
+            # Verify update was called with "No entries loaded"
+            mock_details.update.assert_called_once_with("No entries loaded")
+    
+    def test_update_status_default(self):
+        """Test status bar update with default information."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        mock_parser.get_file_info.return_value = {
+            'path': '/etc/hosts',
+            'exists': True,
+            'size': 100
+        }
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Mock the query_one method
+            mock_status = Mock()
+            app.query_one = Mock(return_value=mock_status)
+            
+            # Add test entries
+            app.hosts_file = HostsFile()
+            app.hosts_file.add_entry(HostEntry(ip_address="127.0.0.1", hostnames=["localhost"]))
+            app.hosts_file.add_entry(HostEntry(
+                ip_address="192.168.1.1", 
+                hostnames=["router"], 
+                is_active=False
+            ))
+            
+            app.update_status()
+            
+            # Verify status was updated
+            mock_status.update.assert_called_once()
+            call_args = mock_status.update.call_args[0][0]
+            assert "Read-only mode" in call_args
+            assert "2 entries" in call_args
+            assert "1 active" in call_args
+    
+    def test_update_status_custom_message(self):
+        """Test status bar update with custom message."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Mock the query_one method
+            mock_status = Mock()
+            app.query_one = Mock(return_value=mock_status)
+            
+            app.update_status("Custom status message")
+            
+            # Verify status was updated with custom message
+            mock_status.update.assert_called_once_with("Custom status message")
+    
+    def test_action_reload(self):
+        """Test reload action."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.load_hosts_file = Mock()
+            app.update_status = Mock()
+            
+            app.action_reload()
+            
+            app.load_hosts_file.assert_called_once()
+            app.update_status.assert_called_with("Hosts file reloaded")
+    
+    def test_action_help(self):
+        """Test help action."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.update_status = Mock()
+            
+            app.action_help()
+            
+            # Should update status with help message
+            app.update_status.assert_called_once()
+            call_args = app.update_status.call_args[0][0]
+            assert "Help:" in call_args
+    
+    def test_action_config(self):
+        """Test config action opens modal."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.push_screen = Mock()
+            
+            app.action_config()
+            
+            # Should push config modal screen
+            app.push_screen.assert_called_once()
+            args = app.push_screen.call_args[0]
+            assert len(args) >= 1  # ConfigModal instance
+    
+    def test_action_sort_by_ip_ascending(self):
+        """Test sorting by IP address in ascending order."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Add test entries in reverse order
+            app.hosts_file = HostsFile()
+            app.hosts_file.add_entry(HostEntry(ip_address="192.168.1.1", hostnames=["router"]))
+            app.hosts_file.add_entry(HostEntry(ip_address="127.0.0.1", hostnames=["localhost"]))
+            app.hosts_file.add_entry(HostEntry(ip_address="10.0.0.1", hostnames=["test"]))
+            
+            app.populate_entries_table = Mock()
+            app.update_status = Mock()
+            
+            app.action_sort_by_ip()
+            
+            # Check that entries are sorted
+            assert app.hosts_file.entries[0].ip_address == "10.0.0.1"
+            assert app.hosts_file.entries[1].ip_address == "127.0.0.1"
+            assert app.hosts_file.entries[2].ip_address == "192.168.1.1"
+            
+            assert app.sort_column == "ip"
+            assert app.sort_ascending is True
+            app.populate_entries_table.assert_called_once()
+    
+    def test_action_sort_by_hostname_ascending(self):
+        """Test sorting by hostname in ascending order."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Add test entries in reverse alphabetical order
+            app.hosts_file = HostsFile()
+            app.hosts_file.add_entry(HostEntry(ip_address="127.0.0.1", hostnames=["zebra"]))
+            app.hosts_file.add_entry(HostEntry(ip_address="192.168.1.1", hostnames=["alpha"]))
+            app.hosts_file.add_entry(HostEntry(ip_address="10.0.0.1", hostnames=["beta"]))
+            
+            app.populate_entries_table = Mock()
+            app.update_status = Mock()
+            
+            app.action_sort_by_hostname()
+            
+            # Check that entries are sorted alphabetically
+            assert app.hosts_file.entries[0].hostnames[0] == "alpha"
+            assert app.hosts_file.entries[1].hostnames[0] == "beta"
+            assert app.hosts_file.entries[2].hostnames[0] == "zebra"
+            
+            assert app.sort_column == "hostname"
+            assert app.sort_ascending is True
+            app.populate_entries_table.assert_called_once()
+    
+    def test_data_table_row_highlighted_event(self):
+        """Test DataTable row highlighting event handling."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.update_entry_details = Mock()
+            
+            # Create mock event with required parameters
+            mock_table = Mock()
+            mock_table.id = "entries-table"
+            event = Mock()
+            event.data_table = mock_table
+            event.cursor_row = 2
+            
+            app.on_data_table_row_highlighted(event)
+            
+            # Should update selected index and details
+            assert app.selected_entry_index == 2
+            app.update_entry_details.assert_called_once()
+    
+    def test_data_table_header_selected_ip_column(self):
+        """Test DataTable header selection for IP column."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            app.action_sort_by_ip = Mock()
+            
+            # Create mock event for IP column
+            mock_table = Mock()
+            mock_table.id = "entries-table"
+            event = Mock()
+            event.data_table = mock_table
+            event.column_key = "IP Address"
+            
+            app.on_data_table_header_selected(event)
+            
+            app.action_sort_by_ip.assert_called_once()
+    
+    def test_restore_cursor_position_logic(self):
+        """Test cursor position restoration logic."""
+        mock_parser = Mock(spec=HostsParser)
+        mock_config = Mock(spec=Config)
+        
+        with patch('hosts.main.HostsParser', return_value=mock_parser), \
+             patch('hosts.main.Config', return_value=mock_config):
+            
+            app = HostsManagerApp()
+            
+            # Mock the query_one method to avoid UI dependencies
+            mock_table = Mock()
+            app.query_one = Mock(return_value=mock_table)
+            app.update_entry_details = Mock()
+            
+            # Add test entries
+            app.hosts_file = HostsFile()
+            entry1 = HostEntry(ip_address="127.0.0.1", hostnames=["localhost"])
+            entry2 = HostEntry(ip_address="192.168.1.1", hostnames=["router"])
+            app.hosts_file.add_entry(entry1)
+            app.hosts_file.add_entry(entry2)
+            
+            # Test the logic without UI dependencies
+            # Find the index of entry2
+            target_index = None
+            for i, entry in enumerate(app.hosts_file.entries):
+                if entry.ip_address == entry2.ip_address and entry.hostnames == entry2.hostnames:
+                    target_index = i
+                    break
+            
+            # Should find the matching entry at index 1
+            assert target_index == 1
+    
+    def test_app_bindings_defined(self):
+        """Test that application has expected key bindings."""
+        with patch('hosts.main.HostsParser'), patch('hosts.main.Config'):
+            app = HostsManagerApp()
+            
+            # Check that bindings are defined
+            assert len(app.BINDINGS) >= 6
+            
+            # Check specific bindings exist (handle both Binding objects and tuples)
+            binding_keys = []
+            for binding in app.BINDINGS:
+                if hasattr(binding, 'key'):
+                    # Binding object
+                    binding_keys.append(binding.key)
+                elif isinstance(binding, tuple) and len(binding) >= 1:
+                    # Tuple format (key, action, description)
+                    binding_keys.append(binding[0])
+            
+            assert "q" in binding_keys
+            assert "r" in binding_keys
+            assert "h" in binding_keys
+            assert "i" in binding_keys
+            assert "n" in binding_keys
+            assert "c" in binding_keys
+            assert "ctrl+c" in binding_keys
+    
+    def test_main_function(self):
+        """Test main entry point function."""
+        with patch('hosts.main.HostsManagerApp') as mock_app_class:
+            mock_app = Mock()
+            mock_app_class.return_value = mock_app
+            
+            from hosts.main import main
+            main()
+            
+            # Should create and run app
+            mock_app_class.assert_called_once()
+            mock_app.run.assert_called_once()