Test a Verilog module via System Verilog

Trying to test a Verilog module via System Verilog. I'm analysing the RTL Simulation and I get the error: Error (10170): Verilog HDL syntax error at Test1.sv(29) near text: "program"; expecting a description.

I tried debugging it, but no results. It shows the error here after I instantiated the module I want to test.

interface valid_in1 (input clk);
logic din;
logic res;
logic out;

modport dut (input clk, din, res, output out);
modport tb (input out, output clk, din, res);

task monitor ();
while (1) begin
@(posedge clk);

if (din==1'b1) begin
$display ("@%0dns res %b out %b din %b clk %b",
$time, res, out, din, clk);
end
 end
endtask
endinterface: valid_in1

module valid (valid_in1.dut din);

valid_in dut (.clk(din.clk),   //the verilog module instantiation
              .din(din.din),
              .res(din.res),
              .out(din.out));         
endmodule

program validprog (valid_in1.tb tin);

default clocking cb @(posedge tin.clk);
endclocking

initial begin
fork
tin.monitor();
join_none
tin.res <= 1;
tin.din <= 0;
##10 tin.res <= 0;
##1 tin.din <= 1;
##10 tin.din <= 0;
##5 $finish;
end
endprogram

module Test1 ();
logic clk= 0;
always #1 clk++;

valid_in1 cin (clk);
valid dut (cin);
validprog tb (cin);
endmodule