Make tests work when running all of them together.

They were only passing when running just the runtime tests, but failing with `<button>undefined</button>` when running all the tests.

test/runtime/samples/action-this/_config.js

@@ -1,10 +1,9 @@
 export default {
-	html: `<button>0</button>`,
-
 	test ( assert, component, target, window ) {
 		const button = target.querySelector( 'button' );
 		const click = new window.MouseEvent( 'click' );
 
+		assert.htmlEqual( target.innerHTML, `<button>0</button>` );
 		button.dispatchEvent( click );
 		assert.htmlEqual( target.innerHTML, `<button>1</button>` );
 	}