feat: make patchright optional, default to stock playwright

tests/test_backend.py

@@ -0,0 +1,45 @@
+"""Unit tests for backend resolution (_resolve_backend)."""
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from cloakbrowser.browser import _resolve_backend
+
+
+def test_resolve_backend_default():
+    """No param, no env var → 'playwright'."""
+    with patch.dict(os.environ, {}, clear=True):
+        assert _resolve_backend(None) == "playwright"
+
+
+def test_resolve_backend_explicit_playwright():
+    assert _resolve_backend("playwright") == "playwright"
+
+
+def test_resolve_backend_explicit_patchright():
+    assert _resolve_backend("patchright") == "patchright"
+
+
+def test_resolve_backend_env_var():
+    """CLOAKBROWSER_BACKEND env var used when no param."""
+    with patch.dict(os.environ, {"CLOAKBROWSER_BACKEND": "patchright"}):
+        assert _resolve_backend(None) == "patchright"
+
+
+def test_resolve_backend_param_beats_env():
+    """Explicit param overrides env var."""
+    with patch.dict(os.environ, {"CLOAKBROWSER_BACKEND": "patchright"}):
+        assert _resolve_backend("playwright") == "playwright"
+
+
+def test_resolve_backend_invalid_raises():
+    with pytest.raises(ValueError, match="Unknown backend 'bogus'"):
+        _resolve_backend("bogus")
+
+
+def test_resolve_backend_invalid_env_raises():
+    with patch.dict(os.environ, {"CLOAKBROWSER_BACKEND": "bogus"}):
+        with pytest.raises(ValueError, match="Unknown backend 'bogus'"):
+            _resolve_backend(None)