Port init elements code

Closes #2 (closed)

tests/__init__.py

+import json
+import sqlite3
+from pathlib import Path
+
+from arkindex_worker.cache import SQL_VERSION
+
+
+def check_json(json_path: Path, elements: list) -> None:
+    assert json_path.is_file()
+
+    assert json.loads(json_path.read_text()) == elements
+
+
+def check_db(db_path: Path, elements: list, images: list) -> None:
+    assert db_path.is_file()
+    db = sqlite3.connect(str(db_path))
+    db.row_factory = sqlite3.Row
+
+    assert list(map(dict, db.execute("select * from version").fetchall())) == [
+        {"version": SQL_VERSION}
+    ]
+    assert (
+        list(map(dict, db.execute("select * from elements order by id").fetchall()))
+        == elements
+    )
+    assert (
+        list(map(dict, db.execute("select * from images order by id").fetchall()))
+        == images
+    )
+
+    db.close()