If variable is blank then no where clause

use OR:

select * from yourTable
where @test = '' OR Agent = @test

if @test coming with null value (instead of ''), you must use:

select * from yourTable
where @test is null OR Agent = @test

And
case when @Status = 1 then tbl1.Status end != 'Done' Or
case when @Status = 2 then tbl1.Status end = 'Done'