How to test linkedserver's connectivity using SQL query

declare @Lnksrvr nvarchar(128), @returnvalue int;
set @Lnksrvr = 'LinkedServer_ConnectionName';
begin try
    exec @returnvalue = sys.sp_testlinkedserver @Lnksrvr;
end try
begin catch
    set @returnvalue = sign(@@error);
end catch;
if @returnvalue <> 0
  raiserror('Unable to connect to server. Please try later!', 16, 2 );
  

SQL Server Function for GetLastDayOfMonth

CREATE FUNCTION [dbo].[fn_GetLastDayOfMonth]     
(    
@InputDate datetime    
)    
RETURNS datetime    
BEGIN    
    RETURN DATEADD(day, -1, DATEADD(month, 1, CAST(CAST(YEAR(@InputDate) AS char(4)) + '/' + CAST(MONTH(@InputDate) AS char(2)) + '/01' AS datetime)))    
END    
  

SQL Server Function for GetFirstDayOfMonth

CREATE FUNCTION [dbo].[fn_GetFirstDayOfMonth]     
(    
@InputDate datetime    
)    
RETURNS datetime    
BEGIN    
    RETURN CAST(CAST(YEAR(@InputDate) AS char(4)) + '/' + CAST(MONTH(@InputDate) AS char(2)) + '/01' AS datetime)    
END