Add a fixture helper for tests

tests/fixtures.py:
Add a fixture helper for tests to easily create a valid repository
database with a few dummy entries.

tests/fixtures.py

+import os
+import shutil
+import tarfile
+import tempfile
+from os.path import dirname, join, realpath
+from pathlib import Path
+
+RESOURCES = join(dirname(realpath(__file__)), "resources", "repo_db")
+
+
+# TODO: rely on pytest-pacman instead of re-inventing the wheel, as soon as there is a release
+def create_db_file(compression: str = "gz", remove_db: bool = False) -> Path:
+    (file_number, db_file) = tempfile.mkstemp(suffix=".db")
+    temp_dir = tempfile.mkdtemp()
+    repo_dir = shutil.copytree(src=RESOURCES, dst=temp_dir, dirs_exist_ok=True)
+
+    with tarfile.open(db_file, f"w:{compression}") as db_tar:
+        os.chdir(repo_dir)
+        for name in ["efivar-37-4", "pacman-5.2.2-1", "elfutils-0.182-1", "libelf-0.182-1"]:
+            db_tar.add(name)
+
+    shutil.rmtree(temp_dir)
+    if remove_db:
+        os.remove(db_file)
+
+    return Path(db_file)