Merge theme detection tests into test_theme_manager

Detection and the manager both live in theme_manager.py, so splitting
their tests across two modules gave no guidance on where a new test
belongs. Keep one test module per module under test.

Author: kaamyashinde

tests/ert/unit_tests/gui/theme_manager/test_theme_detection.py

@@ -2,11 +2,15 @@
 
 import pytest
 from PyQt6.QtCore import Qt
-from PyQt6.QtGui import QGuiApplication
+from PyQt6.QtGui import QColor, QGuiApplication, QPalette
 from PyQt6.QtWidgets import QApplication
 
 from ert.gui.theme_manager import ColorSchemeManager, ColorTheme
 from ert.gui.theme_manager import theme_manager as manager_module
+from ert.gui.theme_manager.theme_manager import (
+    _DARK_BASE_VALUE_THRESHOLD,
+    detect_system_color_theme,
+)
 
 
 @pytest.fixture(autouse=True)
@@ -16,6 +20,12 @@ def _restore_global_stylesheet(qapp):
     qapp.setStyleSheet(original)
 
 
+def _palette_with_base_value(value: int) -> QPalette:
+    palette = QPalette()
+    palette.setColor(QPalette.ColorRole.Base, QColor.fromHsv(0, 0, value))
+    return palette
+
+
 def _pin_system_scheme(monkeypatch, scheme: Qt.ColorScheme) -> None:
     monkeypatch.setattr(QGuiApplication.styleHints(), "colorScheme", lambda: scheme)
 
@@ -26,6 +36,79 @@ def _stub_qss_per_theme(monkeypatch) -> None:
     )
 
 
+@pytest.mark.parametrize(
+    ("reported_scheme", "expected_theme"),
+    [
+        pytest.param(Qt.ColorScheme.Dark, ColorTheme.DARK, id="dark"),
+        pytest.param(Qt.ColorScheme.Light, ColorTheme.LIGHT, id="light"),
+    ],
+)
+def test_that_detection_mirrors_the_scheme_reported_by_style_hints(
+    qtbot, monkeypatch, reported_scheme, expected_theme
+) -> None:
+    hints = QGuiApplication.styleHints()
+    monkeypatch.setattr(hints, "colorScheme", lambda: reported_scheme)
+    assert detect_system_color_theme(hints) == expected_theme
+
+
+def test_that_detection_falls_back_to_palette_when_scheme_is_unknown(
+    qtbot, monkeypatch
+) -> None:
+    hints = QGuiApplication.styleHints()
+    monkeypatch.setattr(hints, "colorScheme", lambda: Qt.ColorScheme.Unknown)
+    # The default Qt palette used in tests has a white base colour (value
+    # 255), which is above _DARK_BASE_VALUE_THRESHOLD, so the fallback path
+    # must resolve to LIGHT.
+    assert detect_system_color_theme(hints) == ColorTheme.LIGHT
+
+
+def test_that_require_style_hints_raises_when_style_hints_are_unavailable(
+    monkeypatch,
+) -> None:
+    monkeypatch.setattr(
+        manager_module.QGuiApplication, "styleHints", staticmethod(lambda: None)
+    )
+    with pytest.raises(RuntimeError, match="styleHints"):
+        manager_module._require_style_hints()
+
+
+def test_that_palette_fallback_returns_light_when_no_qapplication_exists(
+    monkeypatch,
+) -> None:
+    monkeypatch.setattr(
+        manager_module.QApplication, "instance", staticmethod(lambda: None)
+    )
+    assert manager_module._palette_fallback() == ColorTheme.LIGHT
+
+
+@pytest.mark.parametrize(
+    ("base_value", "expected_theme"),
+    [
+        pytest.param(
+            _DARK_BASE_VALUE_THRESHOLD - 1,
+            ColorTheme.DARK,
+            id="returns-dark-when-base-value-is-below-threshold",
+        ),
+        pytest.param(
+            _DARK_BASE_VALUE_THRESHOLD + 1,
+            ColorTheme.LIGHT,
+            id="returns-light-when-base-value-is-above-threshold",
+        ),
+        pytest.param(
+            _DARK_BASE_VALUE_THRESHOLD,
+            ColorTheme.LIGHT,
+            id="returns-light-when-base-value-equals-threshold",
+        ),
+    ],
+)
+def test_that_palette_fallback_resolves_theme_from_base_value_threshold(
+    qtbot, monkeypatch, base_value, expected_theme
+) -> None:
+    app = manager_module.QApplication.instance()
+    monkeypatch.setattr(app, "palette", lambda: _palette_with_base_value(base_value))
+    assert manager_module._palette_fallback() == expected_theme
+
+
 def test_that_apply_raises_runtime_error_when_no_qapplication_exists(
     qtbot, monkeypatch
 ) -> None: