code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.core;
  
  import static org.junit.Assert.assertEquals;
  import static org.junit.Assert.assertFalse;
  import static org.junit.Assert.assertTrue;
  
  import org.junit.After;
  import org.junit.Test;
  
  import java.util.concurrent.TimeUnit;
  
  public class SchedulerTest {
      private static final String DRIFT_USE_NANOTIME = "rx3.scheduler.use-nanotime";
  
      @After
      public void cleanup() {
        // reset value to default in order to not influence other tests
        Scheduler.IS_DRIFT_USE_NANOTIME = false;
      }
  
      @Test
      public void driftUseNanoTimeNotSetByDefault() {
        assertFalse(Scheduler.IS_DRIFT_USE_NANOTIME);
        assertFalse(Boolean.getBoolean(DRIFT_USE_NANOTIME));
      }
  
      @Test
      public void computeNow_currentTimeMillis() {
        TimeUnit unit = TimeUnit.MILLISECONDS;
        assertTrue(isInRange(System.currentTimeMillis(), Scheduler.computeNow(unit), unit, 250, TimeUnit.MILLISECONDS));
      }
  
      @Test
      public void computeNow_nanoTime() {
        TimeUnit unit = TimeUnit.NANOSECONDS;
        Scheduler.IS_DRIFT_USE_NANOTIME = true;
  
        assertFalse(isInRange(System.currentTimeMillis(), Scheduler.computeNow(unit), unit, 250, TimeUnit.MILLISECONDS));
        assertTrue(isInRange(System.nanoTime(), Scheduler.computeNow(unit), TimeUnit.NANOSECONDS, 250, TimeUnit.MILLISECONDS));
      }
  
      private boolean isInRange(long start, long stop, TimeUnit source, long maxDiff, TimeUnit diffUnit) {
        long diff = Math.abs(stop - start);
        return diffUnit.convert(diff, source) <= maxDiff;
      }
  
      @Test
      public void clockDriftCalculation() {
          assertEquals(100_000_000L, Scheduler.computeClockDrift(100, "milliseconds"));
  
          assertEquals(2_000_000_000L, Scheduler.computeClockDrift(2, "seconds"));
  
          assertEquals(180_000_000_000L, Scheduler.computeClockDrift(3, "minutes"));
  
          assertEquals(240_000_000_000L, Scheduler.computeClockDrift(4, "random"));
  
          assertEquals(300_000_000_000L, Scheduler.computeClockDrift(5, null));
      }
  
  }
  