How to use LocalDb database with ADO.NET EDM in WPF project?

Question

WPF

1) I create a new WPF project in Visual Studio Community 2015 (Update 2).
2) Install EntityFramework 6.1.3 via NuGet.
3.1) I add an EDM element, type from the database
3.2) I create a new database "DB", specifying the file in the root of the project (where App.config is), check the box to save the connection settings in App.config
3.3) I include foreign keys (there are no tables yet , but still I put a tick)
3.4) I create a table Test with the fields Id and Name, I update it.
3.5) I add a couple of data records.
3.6) In edmx I update the model from the database, save it. The Test class will be created.
3.7) App.config automatically configured connectionStrings

<connectionStrings>
    <add name="DBEntities" connectionString="metadata=res://*/Model.csdl|res://*/Model.ssdl|res://*/Model.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=(LocalDB)\MSSQLLocalDB;attachdbfilename=|DataDirectory|\DB.mdf;integrated security=True;connect timeout=30;MultipleActiveResultSets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
</connectionStrings>

4) I create the MainVm.cs class (at the root of the project):

using System.Collections.ObjectModel;

namespace DbTest
{
    public class MainVm
    {
        private static readonly DBEntities Entities = new DBEntities();

        public ObservableCollection<Test> Tests { get; set; } = Entities.Test.Local;
    }
}

5) I update MainWindow.xaml:

<Window x:Class="DbTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:DbTest"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:MainVm/>
    </Window.DataContext>
    <Grid>
        <DataGrid ItemsSource="{Binding Tests}"/>
    </Grid>
</Window>

In theory, everything. A table with data should be shown. What did I do wrong or did I forget something?
The list of errors says

No connection string named 'DBEntities' could be found in the application config file

Answer 1

C:\Windows\System32>"C:\Program Files\Microsoft SQL Server\120\Tools\Binn\SqlLocalDB.exe" stop MSSQLLocalDB
DEattach if anything.

Answer 2

private static readonly DBEntities Entities = new DBEntities( database connection string );
connection string like "Data Source=(LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\base.mdf;Integrated Security=True"