编写testbench用于验证上面的cordic_cos

好的，下面是一个简单的testbench，用于验证上面的cordic_cos函数：

`timescale 1ns / 1ns

module test_cordic_cos;

    reg signed [31:0] theta;
    wire signed [31:0] cos_theta;
    wire signed [31:0] expected_cos_theta;

    initial begin
        $monitor("theta=%d, cos_theta=%d, expected_cos_theta=%d", theta, cos_theta, expected_cos_theta);

        #10 theta = 0;
        expected_cos_theta = $signed(32'h7fffffff);
        #10 theta = 8192;
        expected_cos_theta = $signed(32'h00000000);
        #10 theta = 16384;
        expected_cos_theta = $signed(32'h80000000);
        #10 theta = 24576;
        expected_cos_theta = $signed(32'hffffffff);
        #10 theta = 32768;
        expected_cos_theta = $signed(32'h7fffffff);
        #10 theta = 40960;
        expected_cos_theta = $signed(32'h00000000);
        #10 theta = 49152;
        expected_cos_theta = $signed(32'h80000000);
        #10 theta = 57344;
        expected_cos_theta = $signed(32'hffffffff);
        #10 theta = 65536;
        expected_cos_theta = $signed(32'h7fffffff);
        #10 theta = 73728;
        expected_cos_theta = $signed(32'h00000000);
        #10 theta = 81920;
        expected_cos_theta = $signed(32'h80000000);
        #10 theta = 90112;
        expected_cos_theta = $signed(32'hffffffff);
        #10 theta = 98304;
        expected_cos_theta = $signed(32'h7fffffff);
        #10 theta = 106496;
        expected_cos_theta = $signed(32'h00000000);
        #10 theta = 114688;
        expected_cos_theta = $signed(32'h80000000);
        #10 theta = 122880;
        expected_cos_theta = $signed(32'hffffffff);
        #10 $finish;
    end

    cordic_cos cos1(.theta(theta), .cos_theta(cos_theta));

endmodule

testbench中通过向theta输入不同的角度值，验证计算得到的cos_theta值是否与预期值expected_cos_theta一致。在这个testbench中，我们验证了cordic_cos函数在输入的角度分别为0度、90度、180度、270度、360度时的计算结果。