I've got a very simple controller extension that powers an equally simply visualforce page that updates a few fields on the user object, but I have no idea how to go about testing it.  Tried a few different tests and still getting 0% coverage.  Any suggestions on which way to head would be most welcome.

 

public class UserControllerExtension {

private final User usr;

public UserControllerExtension(ApexPages.StandardController stdController) {
this.usr = (User)stdController.getRecord();

}

user u = [SELECT Id, Default_Department_Code__c, Default_Location_Code__c, Default_Funding_Source__c, Default_P_L_Code__c, Include_Opp_Amount_on_FL__c From USER Where Id =:UserInfo.GetuserId()];

public User getUser () {
return u;
}

public PageReference save() {
update u;
return null;
}

}

If I run a flow from within Salesforce using a button, it will display in a lightning skin. However, if I launch that flow via a Visualforce page, it displays with the classic skin. Is there any code I can add to the Visualforce page to make it display in with the lightning skin?