Added fill_mock_backup_dir to create a suitable testing

environment.

tests/fixtures/mock_backupdir.py

@@ -0,0 +1,15 @@
+import pytest
+
+import shutil
+from pathlib import Path
+
+
+def fill_mock_backup_dir(rootdir: Path, target_dir: Path):
+    for property_file in rootdir.glob("*.properties"):
+        shutil.copy2(property_file, target_dir / property_file.name)
+
+    for other_file in filter(
+        lambda path: path.suffix != ".properties", rootdir.glob("*")
+    ):
+        dest = target_dir / other_file.name
+        dest.touch(exist_ok=True)