diff --git a/backend/tests/test_metadata.py b/backend/tests/test_metadata.py
new file mode 100644
index 000000000..732048ec8
--- /dev/null
+++ b/backend/tests/test_metadata.py
@@ -0,0 +1,128 @@
+import json
+import sqlite3
+
+import pytest
+
+from app.database import metadata as metadata_db
+
+
+@pytest.fixture()
+def metadata_database(tmp_path, monkeypatch):
+    db_path = tmp_path / "metadata.sqlite3"
+    monkeypatch.setattr(metadata_db, "DATABASE_PATH", str(db_path))
+    return db_path
+
+
+# Validates that metadata table creation inserts a default empty metadata row.
+def test_create_metadata_table_initializes_empty_metadata(metadata_database):
+    metadata_db.db_create_metadata_table()
+
+    with sqlite3.connect(str(metadata_database)) as conn:
+        rows = conn.execute("SELECT metadata FROM metadata").fetchall()
+
+    assert rows == [("{}",)]
+    assert metadata_db.db_get_metadata() == {}
+
+
+# Validates that creating the metadata table again does not overwrite existing metadata.
+def test_create_metadata_table_preserves_existing_metadata(metadata_database):
+    metadata_db.db_create_metadata_table()
+    expected_metadata = {"user_preferences": {"YOLO_model_size": "medium"}}
+
+    assert metadata_db.db_update_metadata(expected_metadata) is True
+    metadata_db.db_create_metadata_table()
+
+    with sqlite3.connect(str(metadata_database)) as conn:
+        row_count = conn.execute("SELECT COUNT(*) FROM metadata").fetchone()[0]
+
+    assert row_count == 1
+    assert metadata_db.db_get_metadata() == expected_metadata
+
+
+# Validates that metadata retrieval returns None when the table has no metadata row.
+def test_get_metadata_returns_none_when_no_row_exists(metadata_database):
+    metadata_db.db_create_metadata_table()
+
+    with sqlite3.connect(str(metadata_database)) as conn:
+        conn.execute("DELETE FROM metadata")
+
+    assert metadata_db.db_get_metadata() is None
+
+
+# Validates that blank metadata content is treated as missing metadata.
+def test_get_metadata_returns_none_for_blank_metadata(metadata_database):
+    metadata_db.db_create_metadata_table()
+
+    with sqlite3.connect(str(metadata_database)) as conn:
+        conn.execute("UPDATE metadata SET metadata = ?", ("",))
+
+    assert metadata_db.db_get_metadata() is None
+
+
+# Validates that invalid JSON in the metadata row is handled as missing metadata.
+def test_get_metadata_returns_none_for_invalid_json(metadata_database):
+    metadata_db.db_create_metadata_table()
+
+    with sqlite3.connect(str(metadata_database)) as conn:
+        conn.execute("UPDATE metadata SET metadata = ?", ("{invalid-json",))
+
+    assert metadata_db.db_get_metadata() is None
+
+
+# Validates that updating metadata stores nested JSON-compatible values.
+def test_update_metadata_stores_nested_values(metadata_database):
+    metadata_db.db_create_metadata_table()
+    expected_metadata = {
+        "user_preferences": {"YOLO_model_size": "nano", "GPU_Acceleration": False},
+        "recent_folders": ["photos", "archives"],
+        "version": 2,
+    }
+
+    assert metadata_db.db_update_metadata(expected_metadata) is True
+
+    assert metadata_db.db_get_metadata() == expected_metadata
+
+
+# Validates that updating metadata replaces the previous row instead of appending another row.
+def test_update_metadata_replaces_existing_metadata_row(metadata_database):
+    metadata_db.db_create_metadata_table()
+    old_metadata = {"old": True}
+    new_metadata = {"new": True, "count": 3}
+
+    assert metadata_db.db_update_metadata(old_metadata) is True
+    assert metadata_db.db_update_metadata(new_metadata) is True
+
+    with sqlite3.connect(str(metadata_database)) as conn:
+        rows = conn.execute("SELECT metadata FROM metadata").fetchall()
+
+    assert len(rows) == 1
+    assert json.loads(rows[0][0]) == new_metadata
+
+
+# Validates that metadata can be updated through an existing database cursor.
+def test_update_metadata_with_existing_cursor(metadata_database):
+    metadata_db.db_create_metadata_table()
+    expected_metadata = {"bulk_update": True}
+
+    conn = sqlite3.connect(str(metadata_database))
+    try:
+        cursor = conn.cursor()
+        assert metadata_db.db_update_metadata(expected_metadata, cursor) is True
+        conn.commit()
+    finally:
+        conn.close()
+
+    assert metadata_db.db_get_metadata() == expected_metadata
+
+
+# Validates that update failures roll back without deleting previous metadata.
+def test_update_metadata_rolls_back_when_json_serialization_fails(metadata_database):
+    metadata_db.db_create_metadata_table()
+    original_metadata = {"safe": True}
+
+    assert metadata_db.db_update_metadata(original_metadata) is True
+
+    with pytest.raises(TypeError):
+        metadata_db.db_update_metadata({"bad": object()})
+
+    assert metadata_db.db_get_metadata() == original_metadata
\ No newline at end of file
diff --git a/backend/tests/test_yolo_mapping.py b/backend/tests/test_yolo_mapping.py
new file mode 100644
index 000000000..e7228615b
--- /dev/null
+++ b/backend/tests/test_yolo_mapping.py
@@ -0,0 +1,75 @@
+import sqlite3
+
+import pytest
+
+from app.database import yolo_mapping as yolo_mapping_db
+
+
+@pytest.fixture()
+def yolo_database(tmp_path, monkeypatch):
+    db_path = tmp_path / "yolo_mapping.sqlite3"
+    monkeypatch.setattr(yolo_mapping_db, "DATABASE_PATH", str(db_path))
+    return db_path
+
+
+def fetch_mappings(db_path):
+    with sqlite3.connect(str(db_path)) as conn:
+        return conn.execute(
+            "SELECT class_id, name FROM mappings ORDER BY class_id"
+        ).fetchall()
+
+
+# Validates that YOLO class table creation stores each class name with its index.
+def test_create_yolo_classes_table_inserts_class_names(yolo_database, monkeypatch):
+    monkeypatch.setattr(yolo_mapping_db, "class_names", ["person", "bicycle", "car"])
+
+    yolo_mapping_db.db_create_YOLO_classes_table()
+
+    assert fetch_mappings(yolo_database) == [
+        (0, "person"),
+        (1, "bicycle"),
+        (2, "car"),
+    ]
+
+
+# Validates that rerunning table creation does not duplicate existing class mappings.
+def test_create_yolo_classes_table_is_idempotent(yolo_database, monkeypatch):
+    monkeypatch.setattr(yolo_mapping_db, "class_names", ["person", "car"])
+
+    yolo_mapping_db.db_create_YOLO_classes_table()
+    yolo_mapping_db.db_create_YOLO_classes_table()
+
+    assert fetch_mappings(yolo_database) == [(0, "person"), (1, "car")]
+
+
+# Validates that existing class IDs are replaced when class names change.
+def test_create_yolo_classes_table_replaces_existing_class_names(
+    yolo_database, monkeypatch
+):
+    monkeypatch.setattr(yolo_mapping_db, "class_names", ["old-person", "old-car"])
+    yolo_mapping_db.db_create_YOLO_classes_table()
+
+    monkeypatch.setattr(yolo_mapping_db, "class_names", ["person", "car"])
+    yolo_mapping_db.db_create_YOLO_classes_table()
+
+    assert fetch_mappings(yolo_database) == [(0, "person"), (1, "car")]
+
+
+# Validates that table creation succeeds when no YOLO classes are configured.
+def test_create_yolo_classes_table_handles_empty_class_list(yolo_database, monkeypatch):
+    monkeypatch.setattr(yolo_mapping_db, "class_names", [])
+
+    yolo_mapping_db.db_create_YOLO_classes_table()
+
+    assert fetch_mappings(yolo_database) == []
+
+
+# Validates that duplicate class names can be stored under different class IDs.
+def test_create_yolo_classes_table_allows_duplicate_names_with_distinct_ids(
+    yolo_database, monkeypatch
+):
+    monkeypatch.setattr(yolo_mapping_db, "class_names", ["person", "person"])
+
+    yolo_mapping_db.db_create_YOLO_classes_table()
+
+    assert fetch_mappings(yolo_database) == [(0, "person"), (1, "person")]
\ No newline at end of file