feat: harden PDF translation workflow

backend/tests/test_pdf_translate_service.py

@@ -0,0 +1,93 @@
+"""Tests for the resilient PDF translation workflow."""
+
+from app.services.pdf_ai_service import DeepLSettings, PdfAiError, translate_pdf
+
+
+def test_translate_pdf_prefers_premium_provider(monkeypatch):
+    """Should use the premium provider when configured and available."""
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._extract_text_from_pdf",
+        lambda _path: "[Page 1]\nHello world\n\n[Page 2]\nSecond page",
+    )
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._get_deepl_settings",
+        lambda: DeepLSettings(
+            api_key="key",
+            base_url="https://api-free.deepl.com/v2/translate",
+            timeout_seconds=90,
+        ),
+    )
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._translate_with_retry",
+        lambda action, provider_name: action(),
+    )
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._call_deepl_translate",
+        lambda chunk, target_language, source_language=None: {
+            "translation": f"translated::{chunk}",
+            "provider": "deepl",
+            "detected_source_language": "en",
+        },
+    )
+
+    result = translate_pdf("/tmp/demo.pdf", "fr", source_language="en")
+
+    assert result["provider"] == "deepl"
+    assert result["target_language"] == "fr"
+    assert result["detected_source_language"] == "en"
+    assert "translated::" in result["translation"]
+
+
+def test_translate_pdf_falls_back_when_premium_provider_fails(monkeypatch):
+    """Should fall back to OpenRouter if the premium provider fails."""
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._extract_text_from_pdf",
+        lambda _path: "[Page 1]\nHello world",
+    )
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._get_deepl_settings",
+        lambda: DeepLSettings(
+            api_key="key",
+            base_url="https://api-free.deepl.com/v2/translate",
+            timeout_seconds=90,
+        ),
+    )
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._translate_with_retry",
+        lambda action, provider_name: action(),
+    )
+
+    def fail_deepl(*_args, **_kwargs):
+        raise PdfAiError("DeepL unavailable", error_code="DEEPL_SERVER_ERROR")
+
+    monkeypatch.setattr("app.services.pdf_ai_service._call_deepl_translate", fail_deepl)
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._call_openrouter_translate",
+        lambda chunk, target_language, source_language=None: {
+            "translation": f"fallback::{chunk}",
+            "provider": "openrouter",
+            "detected_source_language": "en",
+        },
+    )
+
+    result = translate_pdf("/tmp/demo.pdf", "de", source_language="auto")
+
+    assert result["provider"] == "openrouter"
+    assert result["detected_source_language"] == "en"
+    assert result["translation"].startswith("fallback::")
+
+
+def test_translate_pdf_rejects_identical_languages(monkeypatch):
+    """Should reject no-op translation requests."""
+    monkeypatch.setattr(
+        "app.services.pdf_ai_service._extract_text_from_pdf",
+        lambda _path: "[Page 1]\nHello world",
+    )
+
+    try:
+        translate_pdf("/tmp/demo.pdf", "fr", source_language="fr")
+    except PdfAiError as error:
+        assert error.error_code == "PDF_AI_INVALID_INPUT"
+        assert "different source and target languages" in error.user_message
+    else:
+        raise AssertionError("Expected identical language validation to fail")