module top;
reg clock;
initial begin
clock = 1;
forever #5 clock = ~clock;
end
repeat(30)
@(posedge clock);
$finish;
Tester #(1) t1(clock);
Tester #(2) t2(clock);
Tester #(3) t3(clock);
Tester #(4) t4(clock);
endmodule