feat(websocket): add WebSocket display backend for browser client

tests/test_translate.py

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+"""
+Tests for engine.translate module.
+"""
+
+import json
+from unittest.mock import MagicMock, patch
+
+from engine.translate import (
+    _translate_cached,
+    detect_location_language,
+    translate_headline,
+)
+
+
+def clear_translate_cache():
+    """Clear the LRU cache between tests."""
+    _translate_cached.cache_clear()
+
+
+class TestDetectLocationLanguage:
+    """Tests for detect_location_language function."""
+
+    def test_returns_none_for_unknown_location(self):
+        """Returns None when no location pattern matches."""
+        result = detect_location_language("Breaking news about technology")
+        assert result is None
+
+    def test_detects_berlin(self):
+        """Detects Berlin location."""
+        result = detect_location_language("Berlin police arrest protesters")
+        assert result == "de"
+
+    def test_detects_paris(self):
+        """Detects Paris location."""
+        result = detect_location_language("Paris fashion week begins")
+        assert result == "fr"
+
+    def test_detects_tokyo(self):
+        """Detects Tokyo location."""
+        result = detect_location_language("Tokyo stocks rise")
+        assert result == "ja"
+
+    def test_detects_berlin_again(self):
+        """Detects Berlin location again."""
+        result = detect_location_language("Berlin marathon set to begin")
+        assert result == "de"
+
+    def test_case_insensitive(self):
+        """Detection is case insensitive."""
+        result = detect_location_language("BERLIN SUMMER FESTIVAL")
+        assert result == "de"
+
+    def test_returns_first_match(self):
+        """Returns first matching pattern."""
+        result = detect_location_language("Berlin in Paris for the event")
+        assert result == "de"
+
+
+class TestTranslateHeadline:
+    """Tests for translate_headline function."""
+
+    def test_returns_translated_text(self):
+        """Returns translated text from cache."""
+        clear_translate_cache()
+        with patch("engine.translate.translate_headline") as mock_fn:
+            mock_fn.return_value = "Translated title"
+            from engine.translate import translate_headline as th
+
+            result = th("Original title", "de")
+            assert result == "Translated title"
+
+    def test_uses_cached_result(self):
+        """Translation uses LRU cache."""
+        clear_translate_cache()
+        result1 = translate_headline("Test unique", "es")
+        result2 = translate_headline("Test unique", "es")
+        assert result1 == result2
+
+
+class TestTranslateCached:
+    """Tests for _translate_cached function."""
+
+    def test_translation_network_error(self):
+        """Network error returns original text."""
+        clear_translate_cache()
+        with patch("engine.translate.urllib.request.urlopen") as mock_urlopen:
+            mock_urlopen.side_effect = Exception("Network error")
+
+            result = _translate_cached("Hello world", "de")
+
+            assert result == "Hello world"
+
+    def test_translation_invalid_json(self):
+        """Invalid JSON returns original text."""
+        clear_translate_cache()
+        with patch("engine.translate.urllib.request.urlopen") as mock_urlopen:
+            mock_response = MagicMock()
+            mock_response.read.return_value = b"invalid json"
+            mock_urlopen.return_value = mock_response
+
+            result = _translate_cached("Hello", "de")
+
+            assert result == "Hello"
+
+    def test_translation_empty_response(self):
+        """Empty translation response returns original text."""
+        clear_translate_cache()
+        with patch("engine.translate.urllib.request.urlopen") as mock_urlopen:
+            mock_response = MagicMock()
+            mock_response.read.return_value = json.dumps([[[""], None, "de"], None])
+            mock_urlopen.return_value = mock_response
+
+            result = _translate_cached("Hello", "de")
+
+            assert result == "Hello"