Ng-click - how to unit test for behaviour

When having an angular directive that inside its template has a button with ng-click attribute, should I test the effect of actual action taken (clicking) or of, an attached to ng-click attribute, function call?

In other words, for a directive, that has a template like this:

<div>
    <button ng-click="game.start()">start</button>
</div>

should I test what clicking does or what game.start function does?

I am aware that later the function game.start can be changed for a different one. Also, ng-click can be removed and click event can be caught in a different way.

Unit testing with triggerHandler('click') is tempting but directive's template can also change. That would mean that I need some "proven" access to DOM nodes, namely through id attributes.

Should I attach id attributes on nodes just for unit testing sake or should I take a different aproach to the problem?