Verilog BCD to Seven Segment Decoder

bcd_to_seven_segment_decoder.v

module bcd_to_seven_segment_decoder(
        input [3:0] in,
        output reg a, b, c, d, e, f, g
    );
    always @(in) begin
        case (in)
            0: assign {a, b, c, d, e, f, g} = 7'b1111110;
            1: assign {a, b, c, d, e, f, g} = 7'b0110000;
            2: assign {a, b, c, d, e, f, g} = 7'b1101101;
            3: assign {a, b, c, d, e, f, g} = 7'b1111001;
            4: assign {a, b, c, d, e, f, g} = 7'b0110011;
            5: assign {a, b, c, d, e, f, g} = 7'b1011011;
            6: assign {a, b, c, d, e, f, g} = 7'b1011111;
            7: assign {a, b, c, d, e, f, g} = 7'b1110000;
            8: assign {a, b, c, d, e, f, g} = 7'b1111111;
            9: assign {a, b, c, d, e, f, g} = 7'b1111011;
            default: assign {a, b, c, d, e, f, g} = 7'b0;
        endcase
    end
endmodule

bcd_to_seven_segment_decoder_testbench.v

module bcd_to_seven_segment_decoder_testbench();
    reg [3:0] in;
    wire a, b, c, d, e, f, g;
    
    localparam T = 20;
    
    bcd_to_seven_segment_decoder uut(
        .in(in),
        .a(a), .b(b), .c(c), .d(d), .e(e), .f(f), .g(g)
    );
    
    initial begin
        in <= 0;
        #T;
        if (!a || !b || !c || !d || !e || !f || g)
            $display("assertion failed");
        
        in <= 1;
        #T;
        if (a || !b || !c || d || e || f || g)
            $display("assertion failed");
        
        in <= 2;
        #T;
        if (!a || !b || c || !d || !e || f || !g)
            $display("assertion failed");
        
        in <= 3;
        #T;
        if (!a || !b || !c || !d || e || f || !g)
            $display("assertion failed");
        
        in <= 4;
        #T;
        if (a || !b || !c || d || e || !f || !g)
            $display("assertion failed");
        
        in <= 5;
        #T;
        if (!a || b || !c || !d || e || !f || !g)
            $display("assertion failed");
        
        in <= 6;
        #T;
        if (!a || b || !c || !d || !e || !f || !g)
            $display("assertion failed");
        
        in <= 7;
        #T;
        if (!a || !b || !c || d || e || f || g)
            $display("assertion failed");
        
        in <= 8;
        #T;
        if (!a || !b || !c || !d || !e || !f || !g)
            $display("assertion failed");
        
        in <= 9;
        #T;
         if (!a || !b || !c || !d || e || !f || !g)
            $display("assertion failed");
        
        in <= 10;
        #T;
        if (a || b || c || d || e || f || g)
            $display("assertion failed");
        
        in <= 11;
        #T;
        if (a || b || c || d || e || f || g)
            $display("assertion failed");

        in <= 12;
        #T;
        if (a || b || c || d || e || f || g)
            $display("assertion failed");
        
        in <= 13;
        #T;
        if (a || b || c || d || e || f || g)
            $display("assertion failed");
        
        in <= 14;
        #T;
        if (a || b || c || d || e || f || g)
            $display("assertion failed");
        
        in <= 15;
        #T;
        if (a || b || c || d || e || f || g)
            $display("assertion failed");
        
        $finish;
    end
endmodule

gistfile1.txt

     a     
   -----   
  |     |  
f |     | b
  |  g  |  
   -----   
  |     |  
e |     | c
  |     |  
   -----   
     d     

     a                               a               a                    
   -----                           -----           -----                  
  |     |               |               |               |        |     |  
f |     | b             | b             | b             | b    f |     | b
  |     |               |            g  |            g  |        |  g  |  
                                   -----           -----          -----   
  |     |               |         |                     |              |  
e |     | c             | c     e |                     | c            | c
  |     |               |         |                     |              |  
   -----                           -----           -----                  
     d                               d               d                    

     a               a               a              a               a     
   -----           -----           -----          -----           -----   
  |               |                     |        |     |         |     |  
f |             f |                     | b    f |     | b     f |     | b
  |  g            |  g                  |        |  g  |         |  g  |  
   -----           -----                          -----           -----   
        |         |     |               |        |     |               |  
        | c     e |     | c             | c    e |     | c             | c
        |         |     |               |        |     |               |  
   -----           -----                          -----           -----   
     d               d                              d               d