You are given a four-bit input vector in[3:0]. We want to know some
relationships between each bit and its neighbour:

  (1) out_both: Each bit of this output vector should indicate whether
  both the corresponding input bit and its neighbour to the left (higher
  index) are '1'. For example, out_both[2] should indicate if in[2] and
  in[3] are both 1. Since in[3] has no neighbour to the left, the answer
  is obvious so we don't need to know out_both[3].

  (2) out_any: Each bit of this output vector should indicate whether any
  of the corresponding input bit and its neighbour to the right are '1'.
  For example, out_any[2] should indicate if either in[2] or in[1] are 1.
  Since in[0] has no neighbour to the right, the answer is obvious so we
  don't need to know out_any[0].

  (3) out_different: Each bit of this output vector should indicate
  whether the corresponding input bit is different from its neighbour to
  the left. For example, out_different[2] should indicate if in[2] is
  different from in[3]. For this part, treat the vector as wrapping
  around, so in[3]'s neighbour to the left is in[0].

module TopModule (
  input [3:0] in,
  output [2:0] out_both,
  output [3:1] out_any,
  output [3:0] out_different
);


Reference solution:

module RefModule (
  input [3:0] in,
  output [2:0] out_both,
  output [3:1] out_any,
  output [3:0] out_different
);

  assign out_both = in[2:0] & in[3:1];
  assign out_any = in[2:0] | in[3:1];
  assign out_different = in^{in[0], in[3:1]};

endmodule


Testbench:
`timescale 1 ps/1 ps
`define OK 12
`define INCORRECT 13


module stimulus_gen (
	input clk,
	input tb_match,
	output logic [3:0] in,
	output reg[511:0] wavedrom_title,
	output reg wavedrom_enable	
);


// Add two ports to module stimulus_gen:
//    output [511:0] wavedrom_title
//    output reg wavedrom_enable

	task wavedrom_start(input[511:0] title = "");
	endtask
	
	task wavedrom_stop;
		#1;
	endtask	



	initial begin
		in <= 4'h3;
		@(negedge clk);
		wavedrom_start();
			@(posedge clk) in <= 3;
			@(posedge clk) in <= 6;
			@(posedge clk) in <= 12;
			@(posedge clk) in <= 9;
			@(posedge clk) in <= 5;
		@(negedge clk);
		wavedrom_stop();
		in <= $random;
		repeat(100) begin
			@(negedge clk) in <= $random;
			@(posedge clk) in <= $random;
		end
		#1 $finish;
	end
		
endmodule

module tb();

	typedef struct packed {
		int errors;
		int errortime;
		int errors_out_both;
		int errortime_out_both;
		int errors_out_any;
		int errortime_out_any;
		int errors_out_different;
		int errortime_out_different;

		int clocks;
	} stats;
	
	stats stats1;
	
	
	wire[511:0] wavedrom_title;
	wire wavedrom_enable;
	int wavedrom_hide_after_time;
	
	reg clk=0;
	initial forever
		#5 clk = ~clk;

	logic [3:0] in;
	logic [2:0] out_both_ref;
	logic [2:0] out_both_dut;
	logic [3:1] out_any_ref;
	logic [3:1] out_any_dut;
	logic [3:0] out_different_ref;
	logic [3:0] out_different_dut;

	initial begin 
		$dumpfile("wave.vcd");
		$dumpvars(1, stim1.clk, tb_mismatch ,in,out_both_ref,out_both_dut,out_any_ref,out_any_dut,out_different_ref,out_different_dut );
	end


	wire tb_match;		// Verification
	wire tb_mismatch = ~tb_match;
	
	stimulus_gen stim1 (
		.clk,
		.* ,
		.in );
	RefModule good1 (
		.in,
		.out_both(out_both_ref),
		.out_any(out_any_ref),
		.out_different(out_different_ref) );
		
	TopModule top_module1 (
		.in,
		.out_both(out_both_dut),
		.out_any(out_any_dut),
		.out_different(out_different_dut) );

	
	bit strobe = 0;
	task wait_for_end_of_timestep;
		repeat(5) begin
			strobe <= !strobe;  // Try to delay until the very end of the time step.
			@(strobe);
		end
	endtask	

	
	final begin
		if (stats1.errors_out_both) $display("Hint: Output '%s' has %0d mismatches. First mismatch occurred at time %0d.", "out_both", stats1.errors_out_both, stats1.errortime_out_both);
		else $display("Hint: Output '%s' has no mismatches.", "out_both");
		if (stats1.errors_out_any) $display("Hint: Output '%s' has %0d mismatches. First mismatch occurred at time %0d.", "out_any", stats1.errors_out_any, stats1.errortime_out_any);
		else $display("Hint: Output '%s' has no mismatches.", "out_any");
		if (stats1.errors_out_different) $display("Hint: Output '%s' has %0d mismatches. First mismatch occurred at time %0d.", "out_different", stats1.errors_out_different, stats1.errortime_out_different);
		else $display("Hint: Output '%s' has no mismatches.", "out_different");

		$display("Hint: Total mismatched samples is %1d out of %1d samples\n", stats1.errors, stats1.clocks);
		$display("Simulation finished at %0d ps", $time);
		$display("Mismatches: %1d in %1d samples", stats1.errors, stats1.clocks);
	end
	
	// Verification: XORs on the right makes any X in good_vector match anything, but X in dut_vector will only match X.
	assign tb_match = ( { out_both_ref, out_any_ref, out_different_ref } === ( { out_both_ref, out_any_ref, out_different_ref } ^ { out_both_dut, out_any_dut, out_different_dut } ^ { out_both_ref, out_any_ref, out_different_ref } ) );
	// Use explicit sensitivity list here. @(*) causes NetProc::nex_input() to be called when trying to compute
	// the sensitivity list of the @(strobe) process, which isn't implemented.
	always @(posedge clk, negedge clk) begin

		stats1.clocks++;
		if (!tb_match) begin
			if (stats1.errors == 0) stats1.errortime = $time;
			stats1.errors++;
		end
		if (out_both_ref !== ( out_both_ref ^ out_both_dut ^ out_both_ref ))
		begin if (stats1.errors_out_both == 0) stats1.errortime_out_both = $time;
			stats1.errors_out_both = stats1.errors_out_both+1'b1; end
		if (out_any_ref !== ( out_any_ref ^ out_any_dut ^ out_any_ref ))
		begin if (stats1.errors_out_any == 0) stats1.errortime_out_any = $time;
			stats1.errors_out_any = stats1.errors_out_any+1'b1; end
		if (out_different_ref !== ( out_different_ref ^ out_different_dut ^ out_different_ref ))
		begin if (stats1.errors_out_different == 0) stats1.errortime_out_different = $time;
			stats1.errors_out_different = stats1.errors_out_different+1'b1; end

	end

   // add timeout after 100K cycles
   initial begin
     #1000000
     $display("TIMEOUT");
     $finish();
   end

endmodule