pytest: Verification mode of expanded stmts for the db_write hook

This can be used to find instances of unparseable expanded SQL statements like
the one fixed in #4090

tests/fixtures.py

@@ -17,6 +17,17 @@ class LightningNode(utils.LightningNode):
     def __init__(self, *args, **kwargs):
         utils.LightningNode.__init__(self, *args, **kwargs)
 
+        # If we opted into checking the DB statements we will attach the dblog
+        # plugin before starting the node
+        check_dblog = os.environ.get("TEST_CHECK_DBSTMTS", None) is not None
+        db = os.environ.get("TEST_DB_PROVIDER", "sqlite3")
+        if db == 'sqlite3' and check_dblog:
+            dblog = os.path.join(os.path.dirname(__file__), 'plugins', 'dblog.py')
+            has_dblog = len([o for o in self.daemon.cmd_line if 'dblog.py' in o]) > 0
+            if not has_dblog:
+                # Add as an expanded option so we don't clobber other options.
+                self.daemon.opts['plugin={}'.format(dblog)] = None
+
         # Yes, we really want to test the local development version, not
         # something in out path.
         self.daemon.executable = 'lightningd/lightningd'