sharepoint-online - SpFx + Ribbon function call

Question

I have Sharepoint App which is doing some ribbon customization. Basically, its adding a button within a ribbon. while i can add button successfully, its not invoking my function.

Following is snippet of my Ribbon XML:

<CommandUIHandler Command="ShowHelloWorldCommand" EnabledScript="return true;" CommandAction="test()" />



 public test= () =>
    alert('Hello!');

When ever i click on Ribbon button. it says test is not defined. unfortunately i can not move this function outside on page using content editor or script editor as my test function contains code from Graph Client.

is there a way to invoke function from ribbon ?