Fix #13: Expose Pre-edit Backup restoration

Preserve full diff opcodes before grouping, route modal navigation to a two-axis viewport-sized scroller, and calculate side-by-side layout using terminal cell widths so tabbed Hosts File lines keep a stable divider.

tests/test_backup_restore_modal.py

@@ -0,0 +1,70 @@
+"""Tests for the Pre-edit Backup restoration confirmation."""
+
+import asyncio
+from unittest.mock import Mock
+
+from textual.widgets import Button
+
+from hosts.tui.backup_restore_modal import BackupRestoreModal
+from hosts.core.restore_preview import create_restore_preview
+
+
+async def unchanged_preview(preview):
+    """Return the already reviewed files for modal unit tests."""
+    return preview
+
+
+class TestBackupRestoreModal:
+    """The modal identifies both paths and requires an explicit choice."""
+
+    def test_modal_exposes_backup_and_hosts_file_paths(self, tmp_path):
+        backup = tmp_path / "hosts.backup"
+        hosts_file = tmp_path / "hosts"
+        backup.write_text("127.0.0.1 localhost\n")
+        hosts_file.write_text("192.0.2.1 current.test\n")
+        preview = create_restore_preview(backup, hosts_file)
+        modal = BackupRestoreModal(preview, lambda: unchanged_preview(preview))
+
+        assert modal.preview.backup_path == backup
+        assert modal.preview.hosts_file_path == hosts_file
+
+    def test_confirm_dismisses_true_after_freshness_check(self, tmp_path):
+        backup = tmp_path / "backup"
+        hosts_file = tmp_path / "hosts"
+        backup.write_text("127.0.0.1 restored.test\n")
+        hosts_file.write_text("127.0.0.1 current.test\n")
+        preview = create_restore_preview(backup, hosts_file)
+        modal = BackupRestoreModal(preview, lambda: unchanged_preview(preview))
+        modal.dismiss = Mock()
+        modal._set_status = Mock()
+
+        asyncio.run(modal._confirm())
+
+        modal.dismiss.assert_called_once_with(True)
+
+    def test_cancel_is_focused_and_dismisses_false(self):
+        preview = Mock()
+        modal = BackupRestoreModal(preview, Mock())
+        modal.dismiss = Mock()
+        cancel = Mock()
+        modal.query_one = Mock(return_value=cancel)
+        modal._render_preview = Mock()
+
+        modal.on_mount()
+        modal.action_cancel()
+
+        modal.query_one.assert_called_once_with("#cancel-button", Button)
+        cancel.focus.assert_called_once_with()
+        modal.dismiss.assert_called_once_with(False)
+
+    def test_final_newline_difference_is_visible_without_changed_lines(self, tmp_path):
+        backup = tmp_path / "backup"
+        hosts_file = tmp_path / "hosts"
+        backup.write_bytes(b"127.0.0.1 localhost\n")
+        hosts_file.write_bytes(b"127.0.0.1 localhost")
+        preview = create_restore_preview(backup, hosts_file)
+        modal = BackupRestoreModal(preview, lambda: unchanged_preview(preview))
+
+        rendered = modal._render_diff()
+
+        assert "No newline at end of current Hosts File" in str(rendered)