"More than one element found for locator" warning
Try this instead:
element.all(by.css("ul.nav button")).first()Basically, this tells Protractor that you already know there's more than one element, and you just want the first one (like you said in your question).
The warning is there for a reason. You've tied your tests too closely to your data. The selector is too general & you should be more specific. Either by saying element(by.css("ul.nav button:nth-child(1)")) or scoping your search differently. Protractor tests aren't supposed to be testing style or dom, they're supposed to be testing business logic.