Changing SQL Connection String

ConfigurationManagerWrapper

 public class ConfigurationManagerWrapper : IConfigurationManager
    {
        public NameValueCollection AppSettings
        {
            get
            {
                return ConfigurationManager.AppSettings;
            }
        }

        public string ConnectionStrings(string name)
        {
            return ConfigurationManager.ConnectionStrings[name].ConnectionString;
        }

        public T GetSection<T>(string sectionName)
        {
            return (T)ConfigurationManager.GetSection(sectionName);
        }

        public void ModifyConnectionString(string connectionName, string newConnectionString)
        {
            var config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            config.ConnectionStrings.ConnectionStrings[connectionName].ConnectionString = newConnectionString;
            config.Save();
            ConfigurationManager.RefreshSection("connectionStrings");
        }

    }

DbSwitcherWindowViewModel

  /// <summary>
    /// Allows the connection string to be set in the app.config by the user.  
    /// It will be overwritten by the click once installer when updating, and will need to be set again.
    /// </summary>
    public class DbSwitcherWindowViewModel : BindableBase
    {
        private readonly IMessenger _messenger;
        private readonly ISqlConnectionsWrapper _sqlConnectionsWrapper;
        private readonly IConfigurationManager _configurationManager;
        private const string ConfigConnectionName = "DefaultConnection";
        private string _existingConnectionString;
        private string _newConnectionString;
        private string _message;

        public DbSwitcherWindowViewModel(IMessenger messenger, ISqlConnectionsWrapper sqlConnectionsWrapper, IConfigurationManager configurationManager)
        {
            _messenger = messenger;
            _sqlConnectionsWrapper = sqlConnectionsWrapper;
            _configurationManager = configurationManager;
            ExistingConnectionString = _configurationManager.ConnectionStrings(ConfigConnectionName);
            NewConnectionString = ExistingConnectionString;
            SetConnectionStringCmd = new RelayCommand<string>(UpdateConnectionString);
            TestConnectionCmd = new RelayCommand(TestSqlConnection);
        }

        public string ExistingConnectionString
        {
            get { return _existingConnectionString; }
            set { SetProperty(ref _existingConnectionString, value); }
        }

        public string NewConnectionString
        {
            get { return _newConnectionString; }
            set
            {
                SetProperty(ref _newConnectionString, value);
                ValidateSqlConnectionString();
            }
        }

        public string Message
        {
            get { return _message; }
            set { SetProperty(ref _message, value); }
        }

        public RelayCommand<string> SetConnectionStringCmd { get; set; }
        public RelayCommand TestConnectionCmd { get; set; }

        /// <summary>
        /// Checks to see if connection string can open a Db connection.
        /// </summary>
        private void TestSqlConnection()
        {
            try
            {
                Message = _sqlConnectionsWrapper.TestConnection(NewConnectionString);
            }
            catch (Exception ex)
            {
                Message = ex.Message;
            }
        }

        /// <summary>
        /// Provides a little error checking to see if the format of the connection string is OK...
        /// </summary>
        private void ValidateSqlConnectionString()
        {
            try
            {
                Message = String.Empty;
                _sqlConnectionsWrapper.ValidateConnectionString(NewConnectionString);
            }
            catch (Exception ex)
            {
                Message = ex.Message;
            }
        }
        
        private void UpdateConnectionString(string newConnectionString)
        {
            if (ExistingConnectionString == NewConnectionString) return;
            _configurationManager.ModifyConnectionString(ConfigConnectionName, newConnectionString);
            _messenger.Send("Database connection updated, please restart application.");
        }

    }

SqlConnectionsWrapper

public class SqlConnectionsWrapper : ISqlConnectionsWrapper
    {
        /// <summary>
        /// Wraps SqlConnection class to open a SQL Connection.
        /// </summary>
        /// <param name="connectionString"></param>
        /// <returns></returns>
        public string TestConnection(string connectionString)
        {
            using (var testConn = new SqlConnection(connectionString))
            {
                testConn.Open();
                return "Connection succeeded.";
            }
        }

        /// <summary>
        /// Wraps SqlConnectionStringBuilderClass class to check a connection string for errors.
        /// </summary>
        /// <param name="connectionString"></param>
        /// <returns></returns>
        public void ValidateConnectionString(string connectionString)
        {
            // ReSharper disable once ObjectCreationAsStatement
            new SqlConnectionStringBuilder { ConnectionString = connectionString };
        }

    }