Try following-
<connectionstrings>
<add name="dbconnection" connectionstring="server=Mymachine\SQLSERVER2012; Integrated Security=true; Initial Catalog=Testing" providername="System.Data.SqlClient" />
</connectionstrings>
or,
<connectionstrings>
<add name="dbconnection" connectionstring="Data Source=Mymachine\SQLSERVER2012; Integrated Security=true; Initial Catalog=Testing" providername="System.Data.SqlClient" />
</connectionstrings>
You are missing "server=" or "Data Source=" in your connection string while providing the server name.
Hope, it helps :)