Step 3 complete

tests/services/test_transcription.py

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+"""Tests for transcription.services.transcription."""
+
+from pathlib import Path
+
+import pytest
+
+from transcription.config import Settings
+from transcription.providers.base import ProviderError, TranscriptionResult
+from transcription.services.transcription import (
+    PromptLoadError,
+    TranscriptionError,
+    load_image_payload,
+    load_prompt_text,
+    transcribe_document_image,
+)
+
+
+class _FakeProvider:
+    def __init__(self, *, result: TranscriptionResult | None = None, error: Exception | None = None):
+        self._result = result or TranscriptionResult(
+            text="Transcript output",
+            provider="openrouter",
+            model="test-model",
+        )
+        self._error = error
+        self.calls: list[dict[str, object]] = []
+
+    def transcribe(self, *, prompt_text: str, image_bytes: bytes, mime_type: str) -> TranscriptionResult:
+        self.calls.append(
+            {
+                "prompt_text": prompt_text,
+                "image_bytes": image_bytes,
+                "mime_type": mime_type,
+            }
+        )
+        if self._error:
+            raise self._error
+        return self._result
+
+
+@pytest.mark.unit
+class TestPromptLoading:
+    """Verify prompt artifact loading and validation."""
+
+    def test_loads_prompt_text_from_prompt_dir(self, tmp_path: Path):
+        """Prompt loader returns canonical prompt text from configured prompt directory."""
+        prompt_dir = tmp_path / "prompts"
+        prompt_dir.mkdir()
+        prompt_file = prompt_dir / "transcribe_document.md"
+        prompt_file.write_text("Prompt body", encoding="utf-8")
+
+        settings = Settings(openrouter_api_key="test-key", prompt_dir=prompt_dir)
+        text = load_prompt_text(settings=settings)
+
+        assert text == "Prompt body"
+
+    def test_missing_prompt_raises_error(self, tmp_path: Path):
+        """Prompt loader raises PromptLoadError when the file is missing."""
+        prompt_dir = tmp_path / "prompts"
+        prompt_dir.mkdir()
+
+        settings = Settings(openrouter_api_key="test-key", prompt_dir=prompt_dir)
+        with pytest.raises(PromptLoadError):
+            load_prompt_text(settings=settings)
+
+
+@pytest.mark.unit
+class TestImageLoading:
+    """Verify local image payload loading and mime detection."""
+
+    def test_load_image_payload_reads_bytes_and_mime_type(self, tmp_path: Path):
+        """Image loader returns file bytes and a detected MIME type for supported files."""
+        image_path = tmp_path / "sample.png"
+        image_bytes = b"\x89PNG\r\n\x1a\n"
+        image_path.write_bytes(image_bytes)
+
+        loaded_bytes, mime_type = load_image_payload(image_path)
+
+        assert loaded_bytes == image_bytes
+        assert mime_type == "image/png"
+
+    def test_missing_image_raises_error(self, tmp_path: Path):
+        """Image loader raises TranscriptionError when image file does not exist."""
+        missing = tmp_path / "missing.png"
+
+        with pytest.raises(TranscriptionError):
+            load_image_payload(missing)
+
+
+@pytest.mark.unit
+class TestTranscriptionService:
+    """Verify service orchestration across prompt, image, and provider calls."""
+
+    def test_transcribe_document_image_calls_provider_once(self, tmp_path: Path):
+        """Service loads prompt and image, then invokes provider exactly once."""
+        prompt_dir = tmp_path / "prompts"
+        prompt_dir.mkdir()
+        (prompt_dir / "transcribe_document.md").write_text("Prompt body", encoding="utf-8")
+
+        image_path = tmp_path / "document.jpg"
+        image_path.write_bytes(b"jpeg-bytes")
+
+        settings = Settings(openrouter_api_key="test-key", prompt_dir=prompt_dir)
+        provider = _FakeProvider()
+
+        result = transcribe_document_image(image_path, settings=settings, provider=provider)
+
+        assert result.text == "Transcript output"
+        assert len(provider.calls) == 1
+        assert provider.calls[0]["prompt_text"] == "Prompt body"
+        assert provider.calls[0]["image_bytes"] == b"jpeg-bytes"
+        assert provider.calls[0]["mime_type"] == "image/jpeg"
+
+    def test_provider_error_is_wrapped(self, tmp_path: Path):
+        """Service wraps provider failures in TranscriptionError."""
+        prompt_dir = tmp_path / "prompts"
+        prompt_dir.mkdir()
+        (prompt_dir / "transcribe_document.md").write_text("Prompt body", encoding="utf-8")
+
+        image_path = tmp_path / "document.png"
+        image_path.write_bytes(b"png-bytes")
+
+        settings = Settings(openrouter_api_key="test-key", prompt_dir=prompt_dir)
+        provider = _FakeProvider(error=ProviderError("upstream failure"))
+
+        with pytest.raises(TranscriptionError):
+            transcribe_document_image(image_path, settings=settings, provider=provider)