tests(textframe): Add shutil terminal size detection test

why: Verify display() uses shutil.get_terminal_size() for resize
what:
- Add test_terminal_resize_via_shutil test
- Mock shutil.get_terminal_size to verify it's called

Author: tony

tests/textframe/test_display.py

@@ -0,0 +1,152 @@
+"""Tests for TextFrame.display() interactive viewer."""
+
+from __future__ import annotations
+
+import curses
+import io
+import os
+import typing as t
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from libtmux.textframe import TextFrame
+
+
+class ExitKeyCase(t.NamedTuple):
+    """Test case for exit key handling."""
+
+    id: str
+    key: int | None
+    side_effect: type[BaseException] | None = None
+
+
+EXIT_KEY_CASES: tuple[ExitKeyCase, ...] = (
+    ExitKeyCase(
+        id="quit_on_q",
+        key=ord("q"),
+    ),
+    ExitKeyCase(
+        id="quit_on_escape",
+        key=27,
+    ),
+    ExitKeyCase(
+        id="quit_on_ctrl_c",
+        key=None,
+        side_effect=KeyboardInterrupt,
+    ),
+)
+
+
+@pytest.fixture
+def mock_curses_env() -> t.Generator[None, None, None]:
+    """Mock curses module-level functions that require initscr()."""
+    with (
+        patch("curses.curs_set"),
+        patch("curses.A_REVERSE", 0),
+    ):
+        yield
+
+
+def test_display_raises_when_not_tty() -> None:
+    """Verify display() raises RuntimeError when stdout is not a TTY."""
+    frame = TextFrame(content_width=10, content_height=2)
+    frame.set_content(["hello", "world"])
+
+    with (
+        patch("sys.stdout", new=io.StringIO()),
+        pytest.raises(RuntimeError, match="interactive terminal"),
+    ):
+        frame.display()
+
+
+def test_display_calls_curses_wrapper_when_tty() -> None:
+    """Verify display() calls curses.wrapper when stdout is a TTY."""
+    frame = TextFrame(content_width=10, content_height=2)
+    frame.set_content(["hello", "world"])
+
+    with (
+        patch("sys.stdout.isatty", return_value=True),
+        patch("curses.wrapper") as mock_wrapper,
+    ):
+        frame.display()
+        mock_wrapper.assert_called_once()
+        args = mock_wrapper.call_args[0]
+        assert args[0].__name__ == "_curses_display"
+
+
+@pytest.mark.parametrize("case", EXIT_KEY_CASES, ids=lambda c: c.id)
+def test_curses_display_exit_keys(
+    case: ExitKeyCase,
+    mock_curses_env: None,
+) -> None:
+    """Verify viewer exits on various exit keys/events."""
+    frame = TextFrame(content_width=10, content_height=2)
+    frame.set_content(["hello", "world"])
+
+    mock_stdscr = MagicMock()
+
+    if case.side_effect:
+        mock_stdscr.getch.side_effect = case.side_effect
+    else:
+        mock_stdscr.getch.return_value = case.key
+
+    # Should exit cleanly without error
+    frame._curses_display(mock_stdscr)
+    mock_stdscr.clear.assert_called()
+
+
+def test_curses_display_scroll_navigation(mock_curses_env: None) -> None:
+    """Verify scroll navigation works with arrow keys."""
+    frame = TextFrame(content_width=10, content_height=10)
+    frame.set_content([f"line {i}" for i in range(10)])
+
+    mock_stdscr = MagicMock()
+
+    # Simulate: down arrow, then quit
+    mock_stdscr.getch.side_effect = [curses.KEY_DOWN, ord("q")]
+
+    frame._curses_display(mock_stdscr)
+
+    # Verify multiple refresh cycles occurred (initial + after navigation)
+    assert mock_stdscr.refresh.call_count >= 2
+
+
+def test_curses_display_status_line(mock_curses_env: None) -> None:
+    """Verify status line shows position and dimensions."""
+    frame = TextFrame(content_width=10, content_height=2)
+    frame.set_content(["hello", "world"])
+
+    mock_stdscr = MagicMock()
+    mock_stdscr.getch.return_value = ord("q")
+
+    frame._curses_display(mock_stdscr)
+
+    # Find the addstr call that contains status info
+    status_calls = [
+        call
+        for call in mock_stdscr.addstr.call_args_list
+        if len(call[0]) >= 3 and "q:quit" in str(call[0][2])
+    ]
+    assert len(status_calls) > 0, "Status line should be displayed"
+
+
+def test_curses_display_uses_shutil_terminal_size(mock_curses_env: None) -> None:
+    """Verify terminal size is queried via shutil.get_terminal_size().
+
+    This approach works reliably in tmux/multiplexers because it directly
+    queries the terminal via ioctl(TIOCGWINSZ) on each loop iteration,
+    rather than relying on curses KEY_RESIZE events.
+    """
+    frame = TextFrame(content_width=10, content_height=2)
+    frame.set_content(["hello", "world"])
+
+    mock_stdscr = MagicMock()
+    mock_stdscr.getch.return_value = ord("q")
+
+    with patch(
+        "libtmux.textframe.core.shutil.get_terminal_size",
+        return_value=os.terminal_size((120, 40)),
+    ) as mock_get_size:
+        frame._curses_display(mock_stdscr)
+        mock_get_size.assert_called()