Misuse of Simulator not throwing informative exception message

[quekyj]

I realized that the error message from misuse of Simulator sequence is not helpful. The example below shows the
misuse of unawaited(Simulator.run());. It just shows the test fail. I'm not sure how critical this issue is.

void main() async {
  test('check for value shift', () async {
    final clk = SimpleClockGenerator(10).clk;
    final reset = Logic(name: 'reset');
    final sin = Logic(name: 'sin');

    final shiftReg = ShiftRegister(clk, reset, sin);
    await shiftReg.build();
    // print(shiftReg.generateSynth());

    reset. Inject(1);
    void printFlop([String message = '']) {
      print('@${Simulator.time}:\t'
          ' input=${sin.value}, output '
          '=${shiftReg.sout.value.toString(includeWidth: false)}\t$message');
    }

    // set a max time in case something goes longer
    Simulator.setMaxSimTime(100);

    await clk.nextPosedge;
    sin. Put(1);

    // kick-off the simulator, but we don't want to wait
    unawaited(Simulator.run());
    await clk.nextPosedge;
    printFlop('After sampling 1');

    // we're done, we can end the Simulation
    Simulator.endSimulation();

    await Simulator.simulationEnded;
  });
}

[mkorbel1]

This test has a hang because you have an await clk.nextPosedge; before the Simulator is running. In a test, this will eventually time out and fail, but outside of a context with a timeout this will just hang indefinitely. This type of issue can be tricky to debug, but it's a fundamental trickiness with asynchronous programming in general: if an event never occurs and you wait for it, you just hang. Usually setting a breakpoint and stepping through code can help identify where something might be hanging.