text: #!/usr/bin/env python3
  #
  #  Copyright (c) 2018, The OpenThread Authors.
  #  All rights reserved.
  #
  #  Redistribution and use in source and binary forms, with or without
  #  modification, are permitted provided that the following conditions are met:
  #  1. Redistributions of source code must retain the above copyright
  #     notice, this list of conditions and the following disclaimer.
  #  2. Redistributions in binary form must reproduce the above copyright
  #     notice, this list of conditions and the following disclaimer in the
  #     documentation and/or other materials provided with the distribution.
  #  3. Neither the name of the copyright holder nor the
  #     names of its contributors may be used to endorse or promote products
  #     derived from this software without specific prior written permission.
  #
  #  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  #  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  #  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  #  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
  #  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  #  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  #  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  #  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  #  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  #  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  #  POSSIBILITY OF SUCH DAMAGE.
  
  import time
  import wpan
  from wpan import verify
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Test description: verifies `ChannelManager` channel selection procedure
  
  test_name = __file__[:-3] if __file__.endswith('.py') else __file__
  print('-' * 120)
  print('Starting \'{}\''.format(test_name))
  
  
  def verify_channel(nodes, new_channel, wait_time=20):
      """
      This function checks the channel on a given list of `nodes` and verifies that all nodes
      switch to a given `new_channel` (as int) within certain `wait_time` (int and in seconds)
      """
      start_time = time.time()
  
      while not all([
          (new_channel == int(node.get(wpan.WPAN_CHANNEL), 0)) for node in nodes
      ]):
          if time.time() - start_time > wait_time:
              print('Took too long to switch to channel {} ({}>{} sec)'.format(
                  new_channel,
                  time.time() - start_time, wait_time))
              exit(1)
          time.sleep(0.1)
  
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Creating `wpan.Nodes` instances
  
  # Run the test with 10,000 time speedup factor
  wpan.Node.set_time_speedup_factor(10000)
  
  node = wpan.Node()
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Init all nodes
  
  wpan.Node.init_all_nodes()
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Build network topology
  
  node.form('channel-manager', channel=24)
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Test implementation
  
  all_channls_mask = int('0x7fff800', 0)
  chan_12_to_15_mask = int('0x000f000', 0)
  chan_15_to_17_mask = int('0x0038000', 0)
  
  # Set supported channel mask to be all channels
  node.set(wpan.WPAN_CHANNEL_MANAGER_SUPPORTED_CHANNEL_MASK,
           str(all_channls_mask))
  verify(
      int(node.get(wpan.WPAN_CHANNEL_MANAGER_SUPPORTED_CHANNEL_MASK), 0) ==
      all_channls_mask)
  
  # Sleep for 4.5 second with speedup factor of 10,000 this is more than 12
  # hours.
  time.sleep(4.5)
  
  verify(int(node.get(wpan.WPAN_CHANNEL_MONITOR_SAMPLE_COUNT), 0) > 970)
  
  # Verify the initial value of `NEW_CHANNEL` (should be zero if there has
  # been no channel change so far).
  
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 0)
  
  # Issue a channel-select with quality check enabled, and verify that no
  # action is taken.
  
  node.set(wpan.WPAN_CHANNEL_MANAGER_CHANNEL_SELECT, 'false')
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 0)
  
  # Issue a channel-select with quality check disabled, verify that channel
  # is switched to channel 11.
  
  node.set(wpan.WPAN_CHANNEL_MANAGER_CHANNEL_SELECT, 'true')
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 11)
  verify_channel([node], 11)
  
  # Set channels 12-15 as favorable and request a channel select, verify that channel is switched to 12.
  #
  # Even though 11 would be best, quality difference between 11 and 12 is not high enough for selection
  # algorithm to pick an unfavored channel.
  
  node.set(wpan.WPAN_CHANNEL_MANAGER_FAVORED_CHANNEL_MASK,
           str(chan_12_to_15_mask))
  node.set(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL,
           '25')  # request a channel change to 25
  verify_channel([node], 25)
  node.set(wpan.WPAN_CHANNEL_MANAGER_CHANNEL_SELECT, 'true')
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 12)
  verify_channel([node], 12)
  
  # Set channels 15-17 as favorables and request a channel select, verify that channel is switched to 11.
  #
  # This time the quality difference between 11 and 15 should be high enough for selection
  # algorithm to pick the best though unfavored channel (i.e., channel 11).
  
  node.set(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL,
           '25')  # request a channel change to 25
  verify_channel([node], 25)
  node.set(wpan.WPAN_CHANNEL_MANAGER_FAVORED_CHANNEL_MASK,
           str(chan_15_to_17_mask))
  node.set(wpan.WPAN_CHANNEL_MANAGER_CHANNEL_SELECT, 'true')
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 11)
  verify_channel([node], 11)
  
  # Set channels 12-15 as favorable and request a channel select, verify
  # that channel is not switched.
  
  node.set(wpan.WPAN_CHANNEL_MANAGER_FAVORED_CHANNEL_MASK,
           str(chan_12_to_15_mask))
  node.set(wpan.WPAN_CHANNEL_MANAGER_CHANNEL_SELECT, 'true')
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 11)
  verify_channel([node], 11)
  
  # Starting from channel 12 and issuing a channel select (which would pick 11 as best channel).
  # However, since quality difference between current channel 12 and new best channel 11 is not large
  # enough, no action should be taken.
  
  node.set(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL,
           '12')  # request a channel change to 12
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 12)
  verify_channel([node], 12)
  node.set(wpan.WPAN_CHANNEL_MANAGER_FAVORED_CHANNEL_MASK, str(all_channls_mask))
  node.set(wpan.WPAN_CHANNEL_MANAGER_CHANNEL_SELECT, 'true')
  verify(int(node.get(wpan.WPAN_CHANNEL_MANAGER_NEW_CHANNEL), 0) == 12)
  verify_channel([node], 12)
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Test finished
  
  wpan.Node.finalize_all_nodes()
  
  print('\'{}\' passed.'.format(test_name))
  