return MILLISECONDS;
    }
    if (MICROSECONDS.convert(nanos, NANOSECONDS) > 0) {
      return MICROSECONDS;
    }
    return NANOSECONDS;
  }

  private static String abbreviate(TimeUnit unit) {
    switch (unit) {
      case NANOSECONDS:
        return "ns";
      case MICROSECONDS:
        return "\u03bcs"; // μs
      case MILLISECONDS:
        return "ms";

  }

  public void testElapsed_micros() {
    stopwatch.start();
    ticker.advance(999);
    assertEquals(0, stopwatch.elapsed(MICROSECONDS));
    ticker.advance(1);
    assertEquals(1, stopwatch.elapsed(MICROSECONDS));
  }

  public void testElapsed_millis() {
    stopwatch.start();
    ticker.advance(999999);
    assertEquals(0, stopwatch.elapsed(MILLISECONDS));

  }

  /**
   * Reserves the given number of permits from this {@code RateLimiter} for future use, returning
   * the number of microseconds until the reservation can be consumed.
   *
   * @return time in microseconds to wait until the resource can be acquired, never negative
   */
  final long reserve(int permits) {
    checkPermits(permits);
    synchronized (mutex()) {

  }

  public void testElapsed_micros() {
    stopwatch.start();
    ticker.advance(999);
    assertEquals(0, stopwatch.elapsed(MICROSECONDS));
    ticker.advance(1);
    assertEquals(1, stopwatch.elapsed(MICROSECONDS));
  }

  public void testElapsed_millis() {
    stopwatch.start();
    ticker.advance(999999);
    assertEquals(0, stopwatch.elapsed(MILLISECONDS));

  }

  /**
   * Reserves the given number of permits from this {@code RateLimiter} for future use, returning
   * the number of microseconds until the reservation can be consumed.
   *
   * @return time in microseconds to wait until the resource can be acquired, never negative
   */
  final long reserve(int permits) {
    checkPermits(permits);
    synchronized (mutex()) {

#### The time to answer helps the attackers

  }

  public void testTryAcquire_overflow() {
    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);
    assertTrue(limiter.tryAcquire(0, MICROSECONDS));
    stopwatch.sleepMillis(100);
    assertTrue(limiter.tryAcquire(Long.MAX_VALUE, MICROSECONDS));
  }

  public void testTryAcquire_negative() {
    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);
    assertTrue(limiter.tryAcquire(5, 0, SECONDS));

  }

  public void testTryAcquire_overflow() {
    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);
    assertTrue(limiter.tryAcquire(0, MICROSECONDS));
    stopwatch.sleepMillis(100);
    assertTrue(limiter.tryAcquire(Long.MAX_VALUE, MICROSECONDS));
  }

  public void testTryAcquire_negative() {
    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);
    assertTrue(limiter.tryAcquire(5, 0, SECONDS));

Instead of that, by being an "asynchronous" system, once finished, the task can wait in line a little bit (some microseconds) for the computer / program to finish whatever it went to do, and then come back to take the results and continue working with them.

So, behind the scenes, it will actually work as if everything was the same single app.

///

/// check

You don't have to worry about performance when including routers.

This will take microseconds and will only happen at startup.

So it won't affect performance. ⚡

///

### Include an `APIRouter` with a custom `prefix`, `tags`, `responses`, and `dependencies`