you could use this as a starting point. There maybe minor errors in the framework below:
module adder_tb();
reg clk, reset;
reg [3:0] a,b;
reg carry_in;
wire carry_out;
//adjust your delay according to your reset pulse width
initial begin
clk = 0;
reset = 0;
#20 reset = 1;
#20 reset = 0;
//Insert your stimulus for a,b and carry in here.
//I have just put in an example below
a = 4'b1100;
b = 4'b1011;
carry_in = 1'b1;
#450
a= 4'b1110;
b = 4'b0010;
carry_in = 1'b0;
end
//determine your clock period and adjust the delay below
always #50 clk = ~clk;
//Instantiate your parallel adder here. Example shown below:
adder adder_inst(
.rst(reset),
.clk(clk),
.A(a),
.B(b),
.carry_in(carry_in),
.carry_out(carry_out)
);
endmodule