feat(v2): complete v2 reimplementation

tests/unit/test_execution_transitions.py

@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+import pytest
+from backup_tool.execution import TransitionError, transition
+
+
+@pytest.mark.parametrize(
+    ("current", "target"),
+    [
+        ("queued", "preparing"),
+        ("queued", "cancelled"),
+        ("queued", "failed"),
+        ("preparing", "running"),
+        ("preparing", "cancelling"),
+        ("preparing", "failed"),
+        ("running", "verifying"),
+        ("running", "cancelling"),
+        ("running", "failed"),
+        ("verifying", "committed"),
+        ("verifying", "failed"),
+        ("cancelling", "cancelled"),
+        ("cancelling", "failed"),
+    ],
+)
+def test_all_legal_execution_transitions_are_accepted(current: str, target: str) -> None:
+    assert transition(current, target) == target
+
+
+@pytest.mark.parametrize(
+    ("current", "target"),
+    [
+        ("queued", "running"),
+        ("preparing", "queued"),
+        ("running", "preparing"),
+        ("verifying", "cancelling"),
+        ("cancelling", "running"),
+        ("committed", "cancelled"),
+        ("cancelled", "queued"),
+        ("failed", "queued"),
+        ("unknown", "queued"),
+    ],
+)
+def test_invalid_or_backward_execution_transitions_are_rejected(current: str, target: str) -> None:
+    with pytest.raises(TransitionError) as raised:
+        transition(current, target)
+
+    assert raised.value.code == "invalid_transition"