Add tests that check runtime qt environment selection code

Author: hosaka

tests/test_environment.py

@@ -0,0 +1,82 @@
+"""
+BSD License
+"""
+
+import importlib
+import sys
+import types
+
+import pytest
+from pytest import MonkeyPatch
+
+from qasync import QT_ALL, _get_qt_flavor
+
+
+def _purge_qt(mp: MonkeyPatch):
+    """Ensure no Qt modules are loaded."""
+    for name in QT_ALL:
+        mp.delitem(sys.modules, name, raising=False)
+
+
+def _stub_import(mp: MonkeyPatch, available=()):
+    """Patch importlib.import_module to only 'exist' for certain modules."""
+
+    def fake_import(name):
+        if name in available:
+            return types.ModuleType(name)
+        raise ImportError
+
+    mp.setattr(importlib, "import_module", fake_import)
+
+
+def test_env_exact():
+    with MonkeyPatch.context() as mp:
+        _purge_qt(mp)
+        _stub_import(mp)
+        mp.setenv("QT_API", "PySide6")
+        assert _get_qt_flavor() == "PySide6"
+
+
+def test_env_invalid_raises():
+    with MonkeyPatch.context() as mp:
+        _purge_qt(mp)
+        _stub_import(mp)
+        mp.setenv("QT_API", "QT")
+        with pytest.raises(ImportError):
+            _get_qt_flavor()
+
+
+def test_already_imported_precedence():
+    with MonkeyPatch.context() as mp:
+        _purge_qt(mp)
+        _stub_import(mp)
+        mp.delenv("QT_API", raising=False)
+        mp.setitem(sys.modules, "PySide2", types.ModuleType("PySide2"))
+        mp.setitem(sys.modules, "PyQt5", types.ModuleType("PyQt5"))
+        assert _get_qt_flavor() == next(n for n in QT_ALL if n in ("PyQt5", "PySide2"))
+
+
+def test_first_available_import():
+    with MonkeyPatch.context() as mp:
+        _purge_qt(mp)
+        _stub_import(mp, available=("PySide6",))
+        mp.delenv("QT_API", raising=False)
+        assert _get_qt_flavor() == "PySide6"
+
+
+def test_none_available_raises():
+    with MonkeyPatch.context() as mp:
+        _purge_qt(mp)
+        _stub_import(mp)
+        mp.delenv("QT_API", raising=False)
+        with pytest.raises(ImportError):
+            _get_qt_flavor()
+
+
+def test_env_overrides_imported():
+    with MonkeyPatch.context() as mp:
+        _purge_qt(mp)
+        _stub_import(mp)
+        mp.setitem(sys.modules, "PyQt6", types.ModuleType("PyQt6"))
+        mp.setenv("QT_API", "PySide2")
+        assert _get_qt_flavor() == "PySide2"