What I can test of a Web Api through Unit Testing Project, If my controller return type is HTTPResponseMessage? [on hold]

My Api Code Looks like this.

public HttpResponseMessage GetOffersCities()
{
var response = new HttpResponseMessage();
var objCity = container.Resolve<IOffersRepository>().GetCitiesForOffers();
response.Content = new StringContent(JsonConvert.SerializeObject(objCity));
return response;
}

What basic things I can check in Unit Test Project?