Complementando o post anterior, o erro que ocorre em contexto.Database.CreateIfNotExists(); é
An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in EntityFramework.SqlServer.dll
Additional information: Cannot create file 'C:\Users\Romulo\documents\visual studio 2015\Projects\LojaEF\LojaEF\Loja.mdf' because it already exists. Change the file path or the file name, and retry the operation.
CREATE DATABASE failed. Some file names listed could not be created. Check related errors.
Tentei deletar essa linha de código e executar o novamente. Porém ocorre o mesmo erro em contexto.Usuarios.Add(victor);
Tá complicado...