Add batch photo processing with mode-specific LLM sessions and metadata writes

test/test_metadata_writer.py

@@ -1,5 +1,6 @@
 import shutil
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
 
@@ -211,3 +212,32 @@ def test_set_keywords(make_dng_file, pic, expected_keywords):
 def test_set_keywords_on_existing():
     # TODO
     ...
+
+
+def test_write_caption_and_keywords_in_one_metadata_update(tmp_path):
+    writer = MetadataWriter(tmp_path / "photo.jpg")
+    with (
+        patch.object(writer, "get_caption", return_value="Original caption"),
+        patch.object(writer, "get_keywords", return_value=["existing"]),
+        patch.object(writer, "set_metadata") as set_metadata,
+    ):
+        writer.write(caption="Generated caption", keywords=["architektur"])
+
+    set_metadata.assert_called_once()
+    metadata_tags = set_metadata.call_args.args[0]
+    assert metadata_tags["XMP:Description"] == (
+        f"Original caption. {PREFIX}Generated caption"
+    )
+    assert set(metadata_tags["XMP:Subject"]) == {
+        "existing",
+        f"{PREFIX}architektur",
+    }
+
+
+def test_set_metadata_surfaces_write_failures(tmp_path):
+    writer = MetadataWriter(tmp_path / "photo.jpg")
+    with patch("photools3.metadata_writer.exiftool.ExifToolHelper") as exif:
+        exif_instance = exif.return_value.__enter__.return_value
+        exif_instance.execute.side_effect = OSError("ExifTool failed")
+        with pytest.raises(RuntimeError, match="Could not write metadata"):
+            writer.set_metadata({"XMP:Description": "caption"})