test: add test for new webhook functionality

tests/rpc/test_rpc_webhook.py

@@ -477,3 +477,33 @@ def test_send_msg_discord(default_conf, mocker):
     assert "title" in msg_mock.call_args_list[0][0][0]["embeds"][0]
     assert "color" in msg_mock.call_args_list[0][0][0]["embeds"][0]
     assert "fields" in msg_mock.call_args_list[0][0][0]["embeds"][0]
+
+
+def test_nested_payload_format(default_conf, mocker):
+    webhook_config = {
+        "enabled": True,
+        "url": "https://example.com",
+        "format": "json",
+        "status": {
+            "msgtype": "text",
+            "text": {"content": "Status update: {status}", "contentlist": ["{status}"]},
+        },
+    }
+    default_conf["webhook"] = webhook_config
+
+    webhook = Webhook(RPC(get_patched_freqtradebot(mocker, default_conf)), default_conf)
+
+    msg = {
+        "type": RPCMessageType.STATUS,
+        "status": "running",
+    }
+
+    post = mocker.patch("freqtrade.rpc.webhook.post")
+    webhook.send_msg(msg)
+
+    expected_payload = {
+        "msgtype": "text",
+        "text": {"content": "Status update: running", "contentlist": ["running"]},
+    }
+
+    post.assert_called_once_with("https://example.com", json=expected_payload, timeout=10)