pytest: test for 1M JSONRPC calls which don't need transactions.

diff --git a/tests/plugins/test_libplugin.c b/tests/plugins/test_libplugin.c
index f73378e6..2abf1f7f 100644
--- a/tests/plugins/test_libplugin.c
+++ b/tests/plugins/test_libplugin.c
@@ -197,6 +197,44 @@ static struct command_result *json_checkthis(struct command *cmd,
 	return send_outreq(req);
 }
 
+static struct command_result *spam_done(struct command *cmd, void *unused)
+{
+	return command_success(cmd, json_out_obj(cmd, NULL, NULL));
+}
+
+static struct command_result *spam_errcb(struct command *cmd,
+					 const char *method,
+					 const char *buf,
+					 const jsmntok_t *tok,
+					 void *unused)
+{
+	plugin_err(cmd->plugin, "%.*s",
+		   json_tok_full_len(tok),
+		   json_tok_full(buf, tok));
+}
+
+static struct command_result *json_spamcommand(struct command *cmd,
+					       const char *buf,
+					       const jsmntok_t *params)
+{
+	u64 *iterations;
+	struct request_batch *batch;
+
+	if (!param(cmd, buf, params,
+		   p_req("iterations", param_u64, &iterations),
+		   NULL))
+		return command_param_failed();
+
+	batch = request_batch_new(cmd, NULL, spam_errcb, spam_done, NULL);
+	for (size_t i = 0; i < *iterations; i++) {
+		struct out_req *req = add_to_batch(cmd, batch, "batching");
+		json_add_bool(req->js, "enable", true);
+		send_outreq(req);
+	}
+	return batch_done(cmd, batch);
+}
+
+
 static char *set_dynamic(struct plugin *plugin,
 			 const char *arg,
 			 bool check_only,
@@ -270,6 +308,10 @@ static const struct plugin_command commands[] = { {
 		"checkthis",
 		json_checkthis,
 	},
+	{
+		"spamcommand",
+		json_spamcommand,
+	},
 };
 
 static const char *before[] = { "dummy", NULL };
diff --git a/tests/test_plugin.py b/tests/test_plugin.py
index a036ecc2..b7c2242c 100644
--- a/tests/test_plugin.py
+++ b/tests/test_plugin.py
@@ -4719,3 +4719,23 @@ def test_openchannel_hook_channel_type(node_factory, bitcoind):
         l2.daemon.wait_for_log(r"plugin-openchannel_hook_accepter.py: accept by design: channel_type {'bits': \[12, 22\], 'names': \['static_remotekey/even', 'anchors/even'\]}")
     else:
         l2.daemon.wait_for_log(r"plugin-openchannel_hook_accepter.py: accept by design: channel_type {'bits': \[12\], 'names': \['static_remotekey/even'\]}")
+
+
+@pytest.mark.slow_test
+def test_spam_commands(node_factory, bitcoind):
+    plugin = os.path.join(os.getcwd(), "tests/plugins/test_libplugin")
+    l1 = node_factory.get_node(options={"plugin": plugin, 'log-level': 'info'},
+                               start=False)
+
+    # Memleak detection here creates significant overhead!
+    del l1.daemon.env["LIGHTNINGD_DEV_MEMLEAK"]
+    # Don't bother recording all our io.
+    del l1.daemon.opts['dev-save-plugin-io']
+    l1.start()
+
+    start_time = time.time()
+    l1.rpc.spamcommand(1_000_000)
+    duration = time.time() - start_time
+
+    # Change 100 to 0 to get test to fail so you can see the result!
+    assert duration < 100