Test whole remote backups through a fake ssh command

Real rsync runs over fake ssh and sshpass scripts that execute the remote side locally, covering --link-dest, removal, key file, password and --remote-sudo without a server.

tests/conftest.py

@@ -1,7 +1,8 @@
 """Shared fixtures for the simple_backup tests"""
 
 import sys
-from collections.abc import Callable
+from collections.abc import Callable, Iterator
+from datetime import datetime, timedelta
 
 import pytest
 
@@ -18,6 +19,27 @@ def no_side_effects(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setattr(sb, '_notify', lambda text: None)
 
 
+@pytest.fixture
+def fake_now(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Give each backup a new timestamp, as real runs within the same second would collide"""
+
+    def times() -> Iterator[datetime]:
+        t = datetime(2026, 10, 14, 10, 0, 0)
+
+        while True:
+            yield t
+            t += timedelta(hours=1)
+
+    it = times()
+
+    class FakeDatetime:
+        @staticmethod
+        def now() -> datetime:
+            return next(it)
+
+    monkeypatch.setattr(sb, 'datetime', FakeDatetime)
+
+
 @pytest.fixture
 def run_cli(monkeypatch: pytest.MonkeyPatch) -> Callable[..., int]:
     """Run simple_backup() with the given command line arguments"""