title: forcing a bit in a wire
body: <p>From testbench, I have to corrupt a bus in design.
  I am using a random variable to select a bit location (<code>bit_sel</code>)</p>
  <pre><code>bit_sel = $urandom_range(0,MAX_LENGTH-1);
  </code></pre>
  <p>Bus is somewhere deep inside the RTL with a width of <code>MAXLENGTH</code>.</p>
  <pre><code>wire [MAX_LENGTH-1:0] BUS_TO_BE_FORCED;
  </code></pre>
  <p>In TB, I am using following line to corrupt the bus:</p>
  <pre><code>force TOP.DUT.....BUS_TO_BE_FORCED[bit_sel] = ~TOP.DUT.....BUS_TO_BE_FORCED[bit_sel];
  </code></pre>
  <p>But, I am getting compilation error. What is the best way to do this? I want to flip only one bit.</p>