Add read-only PostgreSQL demotion preparation

tests/test-demote-prepare.py

@@ -0,0 +1,89 @@
+#!/usr/bin/env python3
+
+import importlib.util
+import sys
+import time
+import types
+from pathlib import Path
+
+fake_psycopg2 = types.ModuleType("psycopg2")
+fake_psycopg2.Error = Exception
+fake_psycopg2.OperationalError = OSError
+
+fake_extras = types.ModuleType("psycopg2.extras")
+fake_extras.RealDictCursor = object
+fake_psycopg2.extras = fake_extras
+
+sys.modules["psycopg2"] = fake_psycopg2
+sys.modules["psycopg2.extras"] = fake_extras
+
+spec = importlib.util.spec_from_file_location(
+    "postgresql_plugin",
+    Path("plugins/postgresql/plugin.py"),
+)
+plugin = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(plugin)
+
+runtime_state = {
+    "postgresql": {
+        "notification": {
+            "type": "pre",
+            "operation": "demote",
+            "demote_uname": "david-eve",
+            "promote_uname": "david-prodesk",
+            "received_at": time.time(),
+        },
+    },
+}
+
+result = plugin.demote_prepare(
+    {"PACEMAKER_NODE_NAME": "david-eve"},
+    runtime_state,
+    {},
+)
+
+assert result["ocf_rc"] == 0
+assert result["ready"] is True
+assert result["mutation"] is False
+assert result["successor_node"] == "david-prodesk"
+print("valid_prepare            accepted")
+
+result = plugin.demote_prepare(
+    {"PACEMAKER_NODE_NAME": "david-macbookpro"},
+    runtime_state,
+    {},
+)
+
+assert result["ocf_rc"] == 1
+assert result["reason"] == "local_node_not_target"
+print("wrong_target             rejected")
+
+runtime_state["postgresql"]["notification"]["received_at"] = (
+    time.time() - 121
+)
+
+result = plugin.demote_prepare(
+    {"PACEMAKER_NODE_NAME": "david-eve"},
+    runtime_state,
+    {},
+)
+
+assert result["ocf_rc"] == 1
+assert result["reason"] == "notification_stale"
+print("stale_notification      rejected")
+
+runtime_state["postgresql"]["notification"]["received_at"] = time.time()
+runtime_state["postgresql"]["notification"]["promote_uname"] = ""
+
+result = plugin.demote_prepare(
+    {"PACEMAKER_NODE_NAME": "david-eve"},
+    runtime_state,
+    {},
+)
+
+assert result["ocf_rc"] == 1
+assert result["reason"] == "successor_missing"
+print("missing_successor        rejected")
+
+print()
+print("DEMOTE_PREPARE_TEST_PASS=1")