test(header): cover flush-right clock, date and volume block

tests/test_header.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+import re
+import types
+
+import pytest
+from rich.cells import cell_len
+
+from somafm_tui.widgets.header import HeaderBar
+
+TIME = re.compile(r"\d\d:\d\d:\d\d$")
+DATE = re.compile(r"[A-Z][a-z]{2} \d\d [A-Z][a-z]{2}$")
+VOLUME = re.compile(r"vol \d+%$")
+
+
+def render_header(width: int, height: int = 3) -> list[str]:
+    """Render the header without a running app, as plain text per line."""
+    fake = type("Fake", (), {})()
+    fake.app = types.SimpleNamespace(
+        playing_state="playing", volume=70, current=None, notice=None
+    )
+    fake.size = types.SimpleNamespace(width=width, height=height)
+    return [line.plain.rstrip() for line in HeaderBar.render(fake).renderables]
+
+
+@pytest.mark.parametrize("width", [54, 60, 100, 143, 200])
+def test_right_block_is_flush_right(width: int) -> None:
+    """Clock, date and volume all end on the same column, at the edge."""
+    clock, date, volume = render_header(width)
+    assert [cell_len(line) for line in (clock, date, volume)] == [width] * 3
+    assert TIME.search(clock)
+    assert DATE.search(date)
+    assert VOLUME.search(volume)
+
+
+def test_ragged_middle_does_not_shift_the_right_block() -> None:
+    """"SOMA FM RADIO" and "SAN FRANCISCO" are shorter than
+    "LISTENER SUPPORTED"; the right block must not follow their length."""
+    clock, date, volume = render_header(143)
+    assert cell_len(clock) == cell_len(date) == cell_len(volume) == 143
+
+
+def test_right_block_hidden_on_narrow_terminals() -> None:
+    """Below the threshold the right block is dropped, not squashed."""
+    lines = render_header(30)
+    assert all(":" not in line for line in lines)