tools: Support sending mock messages for non-webhook integrations.

Non-webhook integrations should have fixtures containing mock messages
in json format with fields "subject" and "body" indicating the topic
and content respectively.

tools/generate-integration-docs-screenshot

@@ -29,6 +29,7 @@ from urllib.parse import parse_qsl, urlencode
 
 import orjson
 import requests
+import zulip
 
 from scripts.lib.zulip_tools import BOLDRED, ENDC
 from tools.lib.test_script import prepare_puppeteer_run
@@ -137,6 +138,35 @@ def custom_headers(headers_json: str) -> Dict[str, str]:
         )
 
 
+def send_bot_mock_message(
+    bot: UserProfile, integration: Integration, fixture_path: str, config: BaseScreenshotConfig
+) -> None:
+    # Delete all messages, so new message is the only one it's message group
+    Message.objects.filter(sender=bot).delete()
+    data, _, _ = get_fixture_info(fixture_path)
+
+    assert bot.bot_owner is not None
+    url = f"{bot.bot_owner.realm.uri}"
+    client = zulip.Client(email=bot.email, api_key=bot.api_key, site=url)
+
+    try:
+        request = {
+            "type": "stream",
+            "to": integration.stream_name,
+            "topic": data["subject"],
+            "content": data["body"],
+        }
+        client.send_message(request)
+    except KeyError:
+        print(
+            "{} contains invalid configuration. "
+            'Fields "subject" and "body" are required for non-webhook integrations.'.format(
+                fixture_path
+            )
+        )
+        sys.exit(1)
+
+
 def send_bot_payload_message(
     bot: UserProfile, integration: WebhookIntegration, fixture_path: str, config: ScreenshotConfig
 ) -> bool:
@@ -210,10 +240,13 @@ def generate_screenshot_from_config(
     bot = create_integration_bot(integration, screenshot_config.bot_name)
     create_integration_stream(integration, bot)
     if isinstance(integration, WebhookIntegration):
-        assert isinstance(screenshot_config, ScreenshotConfig)
+        assert isinstance(
+            screenshot_config, ScreenshotConfig
+        ), "Webhook integrations require ScreenshotConfig"
         message_sent = send_bot_payload_message(bot, integration, fixture_path, screenshot_config)
     else:
-        raise AssertionError("Not yet implemented")
+        send_bot_mock_message(bot, integration, fixture_path, screenshot_config)
+        message_sent = True
     if message_sent:
         capture_last_message_screenshot(bot, image_path)
         print(f"Screenshot captured to: {BOLDRED}{image_path}{ENDC}")