make error message more robust

app.py

@@ -42,8 +42,11 @@ def update_run_button(url):
 
 
 def run_testing(user_prompt, invariant_api_key):
+    if not invariant_api_key.startswith("inv"):
+        return "Please enter a valid Invariant API key to get the score!", '', 'toggled-off-button'
+
     agent_params = {"system_prompt": user_prompt}
-    print(agent_params)
+
     yield 'Starting tests...', '', 'button-loading'
     env={
         "INVARIANT_API_KEY": invariant_api_key,