diff --git a/test/functional/test_framework/mininode.py b/test/functional/test_framework/mininode.py
--- a/test/functional/test_framework/mininode.py
+++ b/test/functional/test_framework/mininode.py
@@ -597,8 +597,7 @@
                 self.block_store[block.sha256] = block
                 self.last_block_hash = block.sha256
 
-        reject_reason = [reject_reason] if reject_reason else []
-        with node.assert_debug_log(expected_msgs=reject_reason):
+        def test():
             self.send_message(msg_headers([CBlockHeader(blocks[-1])]))
 
             if request_block:
@@ -611,11 +610,17 @@
                 self.sync_with_ping(timeout=timeout)
 
             if success:
-                wait_until(lambda: node.getbestblockhash()
-                           == blocks[-1].hash, timeout=timeout)
+                wait_until(lambda: node.getbestblockhash() ==
+                           blocks[-1].hash, timeout=timeout)
             else:
                 assert node.getbestblockhash() != blocks[-1].hash
 
+        if reject_reason:
+            with node.assert_debug_log(expected_msgs=[reject_reason]):
+                test()
+        else:
+            test()
+
     def send_txs_and_test(self, txs, node, *, success=True,
                           expect_disconnect=False, reject_reason=None):
         """Send txs to test node and test whether they're accepted to the mempool.
@@ -630,8 +635,7 @@
             for tx in txs:
                 self.tx_store[tx.sha256] = tx
 
-        reject_reason = [reject_reason] if reject_reason else []
-        with node.assert_debug_log(expected_msgs=reject_reason):
+        def test():
             for tx in txs:
                 self.send_message(msg_tx(tx))
 
@@ -651,3 +655,9 @@
                 for tx in txs:
                     assert tx.hash not in raw_mempool, "{} tx found in mempool".format(
                         tx.hash)
+
+        if reject_reason:
+            with node.assert_debug_log(expected_msgs=[reject_reason]):
+                test()
+        else:
+            test()
diff --git a/test/functional/test_framework/test_node.py b/test/functional/test_framework/test_node.py
--- a/test/functional/test_framework/test_node.py
+++ b/test/functional/test_framework/test_node.py
@@ -355,6 +355,18 @@
 
     @contextlib.contextmanager
     def assert_debug_log(self, expected_msgs, unexpected_msgs=None, timeout=2):
+        """Assert that some debug messages are present within some timeout.
+        Unexpected debug messages may be optionally provided to fail a test
+        if they appear before expected messages.
+
+        Note: expected_msgs must always be non-empty even if the goal is to check
+        for unexpected_msgs. This provides a bounded scenario such that "we expect
+        to reach some target resulting in expected_msgs without seeing unexpected_msgs.
+        Otherwise, we are testing that something never happens, which is fundamentally
+        not robust test logic.
+        """
+        if not expected_msgs:
+            raise AssertionError("Expected debug messages is empty")
         if unexpected_msgs is None:
             unexpected_msgs = []
         time_end = time.time() + timeout