Verilog - NAND Gate

 nand_gate.v

module nand_gate(a,b,y);
input a;
input b;
output y;

nand(y,a,b);
endmodule

tb_nand_gate.v

module tb_nand_gate;
reg a;
reg b;
wire y;

nand_gate UUT (.a(a), .b(b), .y(y));

initial begin
$display("Testing NAND gate");

a = 0; b=0;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

a = 0; b=1;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

a = 1; b=0;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

a = 1; b=1;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

$finish;
end
endmodule

The output waveform for nand gate will be as follows: